Roman Basilicas: a Progress Report

C. V. Walthew

University College

Mention Roman basilicas in Italy (or in Ireland, for that matter) and the natural assumption is that you are referring to the great early Christian basilicas like S. Maria Maggiore, S. Clemente or S. Paolo Fuori Le Mura. These buildings, though, stand at the end of a long tradition stretching back at least as far as the 2nd century BC in the Roman Forum and in some of Rome's early colonies in Italy. It was these earlier basilicas, of late-Republican and early-Imperial date, that I was lucky enough to be able to study over a prolonged period during the second half of 1993. What follows is very much an account of work in progress not a definitive statement and the writer reserves his right to change his mind about any or all of it!

It is impossible to study urban development in any part of the Roman Empire without being impressed by the care and precision with which cities were laid out and buildings, both public and private, designed. It is tempting, of course, to look for patterns and modules underlying these designs and earlier work (1) on civil and military buildings in the north-western provinces had suggested that there were, indeed, standard units of measurement, specifically 7.5 and 3.75 pedes Monetales (2) to be detected and that buildings were planned in multiples of these units. It is not unreasonable to suppose that such standard dimensions originated in Italy itself, perhaps even implying centralised drawing-offices in Rome from which blueprints were issued.

But why choose basilicas? Simply because those of the late Republic and early Empire have a compactness, coherence and clarity about their designs which make them suitable for metrological study. All the Italian basilicas considered here, with the probable exception of Iuvanum, shared the basic layout of Vitruvius' basilica at Fano (De Architectura V.1.6), i.e. a central nave surrounded by columns on all four sides, leaving narrower aisles within the side and end walls. Even before serious work began it was perfectly clear that some of these basilicas were virtually identical in size.

The work has not proved to be easy - in fact, the writer seriously underestimated the difficulties involved! Despite the incomparable library facilities in Rome, especially those of the American Academy and the British School, there is a dearth of good information on basilicas. Several are inadequately published, for example Alba Fucens, Iuvanum, Ostia, Roselle, and some are not published at all. The basilica at Cosa, probably the earliest known outside Rome, which was excavated by the American Academy, still awaits its final report after more than forty years. Archaeologists seem reluctant to disclose detailed dimensions of buildings, those that are made known are often inconsistent or inaccurate, and the problem is compounded by the publication of plans at a woefully small scale or even no scale at all (Egnazia in Puglia)!

The only answer, of course, is to examine the buildings themselves on the ground. Those familiar with archaeological survey will be aware of the difficulty of establishing the dimensions of ancient buildings with accuracy, especially when only the foundations or, at best, the lowest courses of the walls survive.

The current archaeological scene in Italy does not help, with standards of maintenance and conservation varying widely in relation to the commitment and financial resources of the local Soprintendenze. Some basilicas (Iuvanum, Lucus Feroniae, Ordona, Saepinum) are well maintained, others (Cosa, Alba Fucens) so heavily overgrown that any attempt to check measurements on the ground is nearly impossible. At Ardea it is thanks only to the commitment of local enthusiasts that a vital early basilica of c. 100 BC has not been totally obliterated since its excavation sixty years ago. And one always has to beware of possible distortions introduced by recent restoration work as at Alba Fucens, Iuvanum, Lucus Feroniae, Ostia, Roselle and Saepinum.

It should be stressed at this point that a basic assumption underlies all that follows, namely that the dimensions of Roman masonry buildings were calculated not in relation to the inner or outer faces of their walls but to their centre-lines. That is to say that a line was first marked out on the ground on which the wall foundations were centred, the faces naturally extending to either side of the line. This is a belief founded on many years' study of the problem, one probably shared by most researchers in this field, but which there is not space to discuss in detail.(3) Similarly, for reasons of economy dimensions are presented here in pedes Monetales (1pM equals 0.29617m.) rather than as actual measurements derived from published sources or work on site. Naturally, detailed arguments and information will be published in full in the final report.

Despite all the pitfalls the exercise proved worthwhile and ten basilicas were examined in detail. The results at first seemed disconcerting. The 7.5 and 3.75pM measurements (or their cubit equivalents) detectable in buildings in the north-western provinces were certainly present, but not extensively or consistently enough to provide a convincing overall explanation. What became abundantly clear (and careful checking and rechecking on the ground and in published sources confirmed this) was that early Roman basilicas in Italy were often not planned in whole numbers of feet but in fractions, resulting in the following peculiar (4) overall dimensions.

Table A: overall dimensions of basilicas calculated in pedes Monetales

1..Alba Fucens (Abruzzo)           180 x 78.75
2..Ardea (Lazio)                   157.5  x 82.5
3..Cosa (Toscana)                  117.25 x 88.75
4..Egnazia (Puglia)                117(N) x 71.25
                                   120 (S)
5..Iuvanum (Abruzzo)(n. 5)         122.75 x 33.75
6..Lucus Feroniae (Lazio)          69 x 48.75
7..Ordona (Puglia)                 142.5 x 93.75
8..Ostia                           140 x 82.5
9..Roselle (Toscana)               105 x 67.5
10..Saepinum (Molise)              ?105 x 63.75
Apart from some obvious and interesting similarities in lengths between Cosa, Egnazia and Iuvanum, Ordona and Ostia, Roselle and Saepinum, these figures at first defied detailed explanation. Finally it dawned that they were, in fact, multiples of the diameters of the columns surrounding the central naves of their respective basilicas. In most cases it was the lower shaft diameter of the columns which seemed to be the relevant factor in determining the overall size of the building, although in one or two the width of column-bases or plinths may rather have been the key. There is, of course, some danger of ambiguity here, a problem yet to be resolved, but in the ruinous state of these buildings it is necessary to accept such evidence as is available. The one exception seems to be Cosa in which the overall dimensions (117.25 x 88.75pM) are multiples of the interaxial spacings of the nave columns, 16.75pM on the long axis and 17.75pM on the short axis, or seven and five times these figures respectively.

To analyse all ten basilicas in detail would require book-length treatment (forthcoming eventually, it is hoped!), so perhaps two examples may suffice:-

(a) Ordona. Early 1st century AD. Columns 8 x 4 (i.e. 8 columns on the long axis of the nave and 4 on the short axis). Lower shaft diameter of columns 3pM. Overall size of nave 105 x 57pM. (35 and 19 times the 3pM shaft diameter respectively). Surrounding aisles 18.75pM wide (6.25 x 3pM - however improbable it may seem 18.75pM is a commonly recurring width for aisles in basilicas and for corridors in buildings of other types: see Tables B and C). Overall length of basilica 142.5pM (47.5 x 3pM) or 161.25pM if the contemporary row of shops at the eastern end of the building is included (53.75 x 3pM) and overall width 93.75pM (31.25 x 3pM).

(b) Saepinum. Late 1st century BC. Columns 8 by 4. Lower shaft diameter of columns 2.5pM. Columns on long axis of nave spaced 7.5pM apart (3 x 2.5pM) and centred at 10pM intervals (4 x 2.5pM). Overall dimensions of nave, long axis: 70pM on column centrings (28 x 2.5pM), 72.5pM including total width of column shafts: (29 x 2.5pM and 73.75pM measured along the column plinths (29.5 x 2.5pM). (see note 6) On the short axis of the nave the corresponding figures are 33.75pM (13.5 x 2.5pM), 36.25pM (14.5 x 2.5pM) and 37.5pM (15 x 2.5pM). Aisles 15pM wide (5 x 2.5pM). Overall length of basilica 105pM (42 x 2.5pM) and overall width 63.75pM (25.5 x 2.5pM). Although 105pM (31.1m.) is the maximum length of the Saepinum basilica currently measurable on the ground, it should be pointed out that the position of the building's SW wall has not been established with absolute certainty. An overall length of 108.75pM (43.5 x 2.5pM) is conceivable, increasing the width of the SW aisle to 18.75pM (7.5 x 2.5pM), What is certain is that the basilica's original width of 63.75pM was later increased to 67.5pM (27 x 2.5pM) by a massive re-enforcement of the main (SE) wall.

What seems to emerge from the figures (if they have been interpreted correctly) is that in both these basilicas the diameters of the lower column shafts, measured just above their bases, provided the numerical basis (3 and 2.5pM respectively) on which were calculated the overall dimensions of the naves, the widths of the enclosing aisles and the lengths of the outer walls of the two buildings. At Saepinum it will have been noticed that the lower shaft diameter even dictated the intervals at which the columns were spaced and the distances separating their central axes (7.5 and 10pM respectively). If the argument that column shaft diameter was crucial to basilica design proves valid, then it becomes possible to see how the apparently strange overall dimensions listed in Table A arose.

Such intricacy in the planning of seemingly simple structures like basilicas may be hard to accept at first sight, but no-one who has studied the complex sets of modules which Vitruvius proposes for the design and construction of temples of all types (De Architectura, Books III-IV, passim) and for public colonnades (Ibid. V. 9.3-4), invariably related to column thickness, will be at all surprised by overall dimensions expressed in fractions of feet rather than whole numbers. And what more likely than that the basilica, a relative latecomer on the architectural scene, should have followed such traditional design concepts, especially given the possibility that as a building type it may have evolved from the public colonnade?

If the conclusion apparently emerging, that the nave columns were fundamental to the overall design of a basilica, proves correct (and a lot of work remains to be done here), then some fascinating implications would seem to follow. For a start, the nave colonnade may have been the first part of the building to be planned. It is noticeable that in discussing the basilica which he designed at Fano Vitruvius (V.1.6) begins with the nave and its columns before proceeding to the aisles and the superstructure of the building. And at one of the basilicas surveyed (Ordona) there is good archaeological evidence to suggest that the foundations of the nave columns were in place before work began on the outer walls of the building.

Secondly, column diameters and spacings may have much to tell us about the origins of the basilica as a building type. Current thinking, with some support from Vitruvius (V.1.4), would envisage the basilica as a later addition to the forum, possibly even an extension or enlargement of the existing colonnade on one side of the square. At Cosa in Etruria the basilica was the final building to be inserted into the layout of the forum, probably c. 150 BC, and its overall size seems to have been determined by the interaxial spacing of its interior columns, whilst both in Italy (Luni in Liguria) and in Spain (Ampurias in Tarraconensis, Conimbriga in Lusitania) basilicas may be seen to have replaced pre-existing colonnades.

But it is for the diffusion of basilicas beyond Italy that column diameter as a factor of overall size may have the most significant potential. Much work remains to be done here too, but as Table B will show, there were some remarkable similarities in size between a whole range of basilicas in Mediterranean provinces.

Table B: Comparative sizes of basilicas in Mediterranean provinces (pM)

Basilica         Cols        Nave       Aisle Width        Overall Size
Augustan        ?8 x 4     82.5 x 37.5      11.25(15)        105 x 67.5
Augustan         8 x 4     70 x 33.75       15        105 (108.75) x 63.75
Baelo (Baetica)
Claudian         8 x 4     76.5 x 33        15               108.75 x 67
c100 BC          9 x 4     120 x 45         18.75            157.5 x 82.5
Augustan           ?       123.75 x 33.75                    157.5 x 78.75
Glanum (Narbonensis)
Julio-Claudian  10 x 4     120 x 42         18.75            157.5 x 79.5
Corinth (N. Basilica)
Augustan        11 x 4     120 x 37.5       18.75            157.5 x 75
Late 1st-       10 x 4     94.5 x 52.5      15           140 (137 5) x 82.5
early 2nd cAD
Corinth (Julian and S. Basilicas)
c.AD 40         ?10 x 4    90 x 40          22.5             135 x 85
Conimbriga (Lusitania)
?Flavian                 8        101.25 x 18.75   15               135 x 48.75
Kempten (Raetia)
Flavian           8        135 x 45         18.75            135 x 82.5
Ruscino (Narbonensis)
Augustan          8 x 4    119.25 x 36      15,22.5          165 x 67.5
Sabratha (Tripolitania)
Flavian 12 x 6 123.75 x 52.5 18.75 165 x 90

The list could be greatly extended, but there may be enough examples here to show a degree of uniformity in the detailed design of these basilicas and to suggest that they were planned on the same basis as those in Italy, possibly even that blueprints were sent from Rome to the provinces to assist local architects in their work. Especially significant in this respect may be the Julian and South Basilicas added to the agora of Corinth c. AD 40, both planned in pM and both identical in every detail.

So far we have concentrated on Italy and the Mediterranean provinces, but if the above arguments have any merit then there should be implications also for the design and dimensions of basilicas in those north-western provinces where the Roman authorities were promoting a policy of urbanisation so vigorously during the first and second centuries AD. Basilicas in these areas of the Empire were, of course, generally larger and later in date than their Mediterranean counterparts, but it was the recurrence of certain measurements in both civilian and military basilicas in the north-west that first prompted the attempt to discern patterns which might ultimately derive from Italy. Some examples are given in Table C.

Table C: Civilian and military basilicas in the north-western provinces (pM)

(1)     Civilian
Basilica                 Overall Size          Nave           Aisle Width
Silchester               285 x 67.5            247.5  x 45        22.5
(masonry basilica)
Wroxeter                 258.75 x 82.5         217.5 x 45         18.75
Xanten Colonia           247.5 x 63.75
(baths' basilica)
Tarraco                  240 x ?108.75         195 x 52.5         22.5
Feurs                    232.5 x 78.75         195 x 41.25        18.75
Caistor-by-Norwich       187.5 x 52.5          168.75 x 33.75     15
Caerwent                 187.5 x 67.5          135 x 30           18.75
(2)     Military
Chester principia              247.5 EW
Caerleon                 217.5 x 86.25         217.5 x 41.25      22.5
Caerleon                 225  x 97.5           165 x 52.5         22.5
(principia cross-hall)  (217.5 int.)
Vetera 1 (Xanten)        217.5 x 90            172.5 x 45         22.5
(principia cross-hall)
Chester                  270 x 86.25           270 x 41.25        22.5
(bath's basilica)

Here it will be noted that the length of the Silchester nave matches the overall sizes of the Chester principia and the Xanten baths' basilica; that the Wroxeter nave corresponds to that of the Caerleon baths' basilica (and to its overall size), to the internal length of the Caerleon principia cross-hall and to the total length of the cross-hall of the Vetera 1 principia; and that there are close similarities in dimensions between the civilian basilicas at Caerwent and Caistor-by-Norwich on the one hand and Feurs and Tarraco on the other.

Naturally, much of the detail underlying these similarities has yet to be clarified, but there seems no denying a close relationship between the planning of civil and military basilicas in the north-western Empire. This, of course, touches upon one of the hottest recent controversies in Roman provincial archaeology, namely, which influenced the other? Major obstacles here are the relatively late dates of masonry basilicas in the north-western Empire, the lack of securely dated examples in central and northern Gaul which could provide the missing links in the chain of diffusion and our present ignorance of the designs of the wooden predecessors which might be expected in the north-European context (Silchester is a promising exception here). At the moment it seems safest to suppose that, although the designs of both civilian and military basilicas may be ultimately of Italian (and probably urban) origin, nevertheless in the relatively under-developed north-west the army must have played a vital role as the main, if not sole, source of the necessary expertise in planning and construction and it is hoped that further detailed analysis may shed more light upon this.

Much of this article has focused upon measurements and this fairly reflects the writer's main interests, but any in-depth study of basilicas is bound to touch upon other aspects of their design, construction and functions. There is, for example, the question of the nave superstructure, generally assumed to have taken the form of a clerestory rising about the roofs of the flanking aisles and implying a two-storey colonnade surrounding the nave or a single giant order rising to roof level, as in Vitruvius' basilica at Fano.

The discovery of column shafts and/or bases of two different diameters inside the Ardea and Ostia basilicas, two different types of capital at Baelo and the massive foundations provided for the nave columns at Baelo and Ordona would tend to suggest that the general assumption is correct (though denied, remarkably, in the only detailed study of Ordona despite the 2.45m./8 ft. depth of the column foundations!). Then there is the location of the tribunal for the magistrates. What seems to have been the front of a podium 9.36m. wide projecting slightly (60cm.) into the eastern aisle of the Egnazia basilica from the building's narrow eastern end and flanked by a doorway on its northern side looks a promising candidate here (7) and the possibility (noted above) that the aisle at the narrow south-western end of the Saepinum basilica was wider than the other three might well imply extra space for interested parties to congregate or sit in front of a tribunal.

But most interesting of all, and the focus of much recent research, is the provision of a room located centrally at the rear of basilicas facing across the width of the building towards the main facade. Such a room was already an integral, if small, part of the basilica at Cosa c. 150 BC and had become a regular, generally much enlarged, feature of basilica design by the late 1st. century BC (Iuvanum, Ordona, Roselle, Saepinum). The room has often been interpreted as tribunal or council-chamber (curia), but its spaciousness (especially in and after the Augustan period), expensive fittings and the discovery of imperial portrait statues in or close to it has also suggested an equation with the temple of Augustus (aedes Augusti) as planned by Vitruvius for his basilica at Fano (fig. 1). One only has to notice the massive size of this room at Roselle, its floor raised high above the level of the relatively small-scale basilica which it adjoins to be impressed by this interpretation.

But it is perhaps at Lucus Feroniae that the impact of the aedes Augusti on the design of a basilica can be most graphically illustrated. This basilica had probably been in existence since the closing decades of the Republic, its high platform dominating the northern end of the forum. The aedes was added to the rear of the building seemingly in the Augustan period, but not on its central axis from which it was displaced slightly to the west by a small pre-existing Republican temple. It took the form of an apsidal room over 6 m. long paved with mosaic, the side walls of which (to W and E) were each flanked by four pedestals, while two larger bases occupied the apse (to N). The pedestals and bases had, it seems carried statues of Augustus, Agrippa and other members of the Julio-Claudian house.

The addition of the aedes brought significant changes to the nave of the basilica in that a column was omitted on its northern side (Vitruvius stipulated the omission of two in the corresponding position in his much larger basilica at Fano: V. 1.7) thus creating a clear, if diagonal line of sight leading to the aedes entrance from a platform projecting into the forum from the centre of the building's main (south) facade. This diagonal approach to the temple of Augustus was reflected in the correspondingly oblique alignment of a pair of statue bases at the foot of the nave's NW and NE corner columns and may have been intended to maintain a visual link with the much earlier altar of the goddess Feronia standing in its own precinct on the SE side of the forum. Whether this suggestion is correct or not, the introduction of the aedes Augusti at Lucus Feroniae was clearly part of a wider policy evolving in the Julio-Claudian period to create a more formal and ceremonial role for basilicas in Italy and the provinces and thereby enhance the prestige of the Emperor and his family.

As stated at the beginning, the purpose of this article has not been to reach conclusions but to describe work in progress by sketching some of the ways in which, it is hoped, further research may illuminate the detailed planning and construction, the origins, diffusion and changing functions of a particularly important type of Roman public building.


1. C.V. Walthew, 'Possible standard units of measurement in Roman military planning' Britannia 12 (1981). 15-35; 'Length-units in house-planning at Silchester and Caerwent', ibid 18 (1987), 201-231; 'Length-units in Roman military planning: Inchturhil and Colchester' Oxford Journal of Archaeology 7 (1988), 81-98. See also the cautionary remarks of R.P. Duncan-Jones, 'Length-units in Roman town planning' Britannia 11 (1980), 127-133. On basilicas see John Carter, 'Civic and other buildings' in I.M. Barton ed. Roman Public Buildings 1989, 41-43.
2. = 2.22m and 1.11m respectively or perhaps their equivalents in cubits: 5 and 2.50.
3. For a detailed review of the problem see P. Huggins, K. Rodwell and W. Rodwell in P.J. Drury ed. Structural Reconstruction BAR 110 (1982), 21-65, esp. p.53.
4. Peculiar to us, perhaps, but not to the Romans, as can be seen from the Orange (Arausio) cadastral inscription in which properties occupying a street-frontage of the colonia were divided up on the following basis: 18, 34.5, 35, 55.5 and 75 pM.
5. Iuvanum differed from the other Italian basilicas reviewed here in not containing an internal colonnade, despite recent suggestions to the contrary, but comprising a simple hall 123.75 pM long by 33.75 pM wide, the overall length of which was extended to 157.5 pM by annexes at the east and west ends. On the northern side of the hall lay an imposing apsidal room, either the curia or aedes Augusti see below), which would increase the overall width of the building to 78.75 pM (86.25 pM including the apse).
6. On the NW side of the nave. The corresponding figure on the SE. side was 74.75 pM. It is tempting to suppose that the nave was originally planned as 75 x 37.5 pM, resp. 30 and 15 x 2.5 pM. If so, the plan was not fully executed on the ground.
7. Especially since it is fronted by a central intercolumniation in the eastern colonnade of the nave which is 0.5 pM wider than the other two.
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