The Pantheon: From Antiquity to the Present
Page 24
Mix mortard 0.55 mdays/m³ 1,950 1,290 1,310 1,860 1,340 7,750
Fetch materials 0.164 mdays/m³ 1,560 1,160 1,100 1,320 850 5,990
Lay foundationse 0.384 mandays/m³ 5,350 5,350
Lay facef 800 (1,000*) pieces/day x 1.5 for assistant 36* 684 332 254 1310
Lay coreg 4.01 + 0.12 (ht – 1) mdays/m³ x 1.5 for assistant 8,440 40,300 38,400 67,500 154,500
Lay core for dome 2.68 + 0.08 (ht – 1) mdays/m³ x 1.5 for assistant 53,500 53,500
Lay arches and bonding coursesh 200 bricks/day x 1.5 for assistant 240 1,010 591 67 1,910
Raising materialsi 0.12 mdays/m³ x (ht – 1) 700 3,410 3,100 1,350 8,560
Erect scaffoldingj 0.063 mdays/m² face 334 206 334 300 1,170
Formwork for vaultsk 0.2 (0.4*) mdays/m² 27 470 799 1,740* 3,040
Subtotal 20,500 45,300 46,700 76,300 59,600 248,000
Supervision 10% of total 2,050 4,530 4,670 7,630 5,960 24,800
Shaping orders 16,900 2,470 19,400
Moving and lifting ordersl 1,480 756 2,240
TOTAL 22,500 68,200 54,600 84,000 65,600 295,000
* * *
a Pegoretti 1869, vol. 1, pp. 240–245, for the whole process of digging foundations.
b Pegoretti 1869, vol. 1, p. 157.
c Pegoretti 1869, vol. 2, p. 131.
d Pegoretti 1869, vol. 2, p. 144.
e Pegoretti 1869, vol. 2, p. 144.
f DeLaine 1997, no. 3, pp. 268–269, note 5. The higher figure indicated by an asterisk is for the rougher brickwork in the substructures.
g Pegoretti 1869, vol. 2, pp. 144–145.
h Pegoretti 1869, vol. 2, p. 156, and DeLaine 1997, no. 3, p. 176.
i Pegoretti 1869, vol. 1, p. 243.
j Pegoretti 1869, vol. 2, pp. 6–7, for all details of scaffolding.
k Pegoretti 1869, vol. 2, p. 209, for all details of vault centering. The higher figure is for the more complex vaults.
l Pegoretti 1869, vol. 2, pp. 14–15.
Table 6.2. Manpower for building the intermediate block in mandays (mdays) of labor
* * *
Intermediate blockFoundationsLower zoneMiddle zoneUpper zoneTotal
Quantities
Total volume (m³) 933 1,340 1,175 509 4,000
Brick pieces in facing 3,420 64,300 52,600 57,000 177,000
Actions Rate mdays/m³ Total mdays Total mdays Total mdays Total mdays Total mdays
Excavate in rocky ground to 1.6 m 0.165 mdays/m³ 37 37
Excavate below 1.6 m 0.248 mdays/m³ 175 175
Remove debris over 50 m 0.164 mdays/m³ 153 153
Slake lime for mortar 1.2 mdays/m³ 99 104 143 67 412
Mix mortar 0.55 mdays/m³ 249 250 439 206 1,140
Fetch materials 0.164 mdays/m³ 199 220 748 352 1,520
Lay foundations 0.384 mdays/m³ 196 358
Lay face 800 pieces/day x 1.5 for assistant 5 121 177 29 332
Lay core 4.01 + 0.12 (ht – 1) mdays/m³ x 1.5 for assistant 1,240 7,810 9,040 4,260 22,400
Lay arches and bonding courses 200 bricks/day x 1.5 for assistant 34 20 30 84
Raising materials 0.12 mdays/m³ x (ht – 1) 114 487 229 830
Erect scaffolding 0.063 mdays/m² of face 59 50 54 163
Formwork for vaults 0.2 mdays/m² 11 28 27 66
Subtotal 2,520 8,720 11,100 5,250 27,600
Supervision 10% of total 250 870 1,110 525 2,760
TOTAL 2,770 9,590 12,200 5,780 30,400
* * *
Table 6.3. Manpower for building the portico in mandays (mdays) of labor
* * *
PorticoFoundationsColumnsEntablaturePedimentRoof
Action Rate Total mdays Total mdays Total mdays Total mdays Total mdays Total mdays
Excavate in rocky ground to 1.6 m 0.165 mdays/m³ 38 38
Excavate below 1.6 m 0.248 mdays/m³ 180 180
Remove debris over 50 m 0.164 mdays/m³ 157 157
Slake lime for mortar 1.2 mdays/m³ 78 78
Mix mortar 0.55 mdays/m³ 198 198
Fetch materials 0.164 mdays/m³ 157 3 160
Lay foundations 0.384 mdays/m³ 368 368
Tie up blocks with ropesa 0.03/0.033 mdays/m³ x 5 men 88 52 56 32 228
Place on rollers 0.025/0.0275 mdays/m³ x 5 men 73 43 47 24 187
Move large items 50 m 0.003days/m x 50 m x (5 + (wt – 5t)/1.25) men 207 125 128 203 663
Raise and put in place 0.025 days/m x ht x (11 + wt/0.625) men 627 889 1,020 1,590 4,130
Lay roof 0.22 mdays/m3 + 1.625 mdays/m2 759 759
Subtotal 1,180 995 1,110 1,250 2,610 7,150
Supervision 10% of total 118 included included included included 118
Shape stone and marble elements 33,600 4,940 1,620 40,200
TOTAL 1,300 34,600 6,050 2,870 2,610 47,500
* * *
a Pegoretti 1869, vol. 2, pp. 14–15, for this and all other formulae for moving and raising large blocks.
Table 6.4. Manpower for building the grottoni in mandays (mdays) of labor
* * *
GrottoniFoundationsLower zoneMiddle zoneUpper zoneTotal
Quantities
Total volume (m³) 1,070 1,330 1,260 526 4,190
Number of brick pieces in facing 91,200 89,000 57,000 237,000
Action Rate mdays/m³ Total mdays Total mdays Total mdays Total mdays Total mdays
Excavate in rocky ground to 1.6 m 0.165 mdays/m³ 43 43
Excavate below 1.6 m 0.248 mdays/m³ 202 202
Remove debris over 50 m 0.164 mdays/m³ 176 176
Slake lime for mortar 1.2 mdays/m³ 87 105 98 28 318
Mix mortar 0.55 mdays/m³ 222 319 304 89 934
Fetch materials 0.164 mdays/m³ 176 218 202 86 682
Lay foundations 0.384 mdays/m³ 412 412
Lay face 800 pieces/day x 1.5 for assistant 171 168 15 354
Lay corea 4.03 + 0.12 (ht – 1) mdays/m³ x 1.5 for assistant 7,870 8,400 3,260 19,530
Lay arches and bonding courses 200 bricks/day x 1.5 for assistant 45 15 98 158
Raising materials 0.12 mdays/m³ x (ht–1) 73 175 123 371
Erect scaffolding 0.063 mdays/m² of face 93 84 20 197
Formwork for vaults 0.2 mdays/m² of face 106 98 54 219
Subtotal 1,320 9,000 9,540 3,770 23,600
Supervision 10% of total 132 900 954 377 2,360
TOTAL 1,450 9,900 10,500 4,150 26,000
* * *
a Pegoretti 1869, vol. 2, pp. 144–145. The figure is slightly higher than for the rotunda because of the relative thinness of the walls.
Scheduling the Work
Construction on the whole is a logical process, where the sequence of events is largely determined by structural necessity, the inexorable demands of gravity, and the behavior of materials. Within these limits, however, there are usually several different ways in which the work can be scheduled, especially in complex projects like the Pantheon with its four potentially independent units. In addition, certain construction processes require the cessation of work for a period of time. As concrete gains strength only over time, it is not possible that the whole of the fabric of the rotunda could have gone up in a single season. The builders would have wanted to be sure that the strength of the concrete was sufficiently developed before laying the drum on the foundations, and before erecting the dome on the drum, making these obvious places for a fairly lengthy cessation of work. Additional stages are also highly likely, as argued later.
The first steps in construction are obviously the groundworks and foundations. The archaeological and constructional evidence suggests that all of the foundations of the rotunda, intermediate block, and portico were created at the same time, but that those of the grottoni, which abut those of the rotunda, were added partway through construction.25
While the sequence of construction for the rotunda itself is reasonably self-evident, a few points need to be made here. The first is that the three divisions, coinciding with the three exterior cornices, would appear to mark natural breaks in construction (Fi
g. 6.3). On the interior, the lowest corresponds with the top of the frieze of the main order. The insertion of the lower columnar order would have necessitated a hiatus in the construction of the drum, since the order is an integral part of the structure and both architrave/frieze and cornice blocks are embedded in its concrete walls. For these heavy marble blocks to be supported by the concrete, the drum probably needed to have gained more strength than ordinarily required to support the next lift of concrete, although exactly how long this would have taken cannot be determined.26 The same applies to the cornice blocks of the interior attic zone, which project strongly and thus need to be deeply embedded in the walls. Although the upper zone of the drum on the inside forms the lower part of the dome, this part is almost vertical and could easily have been built by gently cantilevering out each lift of concrete (see Chapters Four and Seven). The need for the whole drum and lower part of the dome to gain most of its strength before the upper part of the dome was added introduces another necessary hiatus in construction.
The situation is more complicated with the other three elements of the building, as, for example, the lower walls of the grottoni and the upper walls of the intermediate block abut the rotunda and must have been built later than it. Although the intermediate block was clearly planned as an integral part of the Pantheon, it is only bonded to the rotunda up to roughly the level of the first exterior cornice, so that the rest cannot have been completed until after the drum was finished.27 Since there are no structural reasons for the intermediate block not to be bonded to the rotunda, it is reasonable to assume that there was a gap of a season or more. Exactly how long after the rotunda was finished is impossible to determine, but the similarities in the brickstamps make it clear that not much time elapsed. The inverse situation prevails for the grottoni, where the structure seems not to have been part of the original plan, but was added partway through the construction of the rotunda, perhaps for structural reasons.28 Here, only the bridge is bonded to the rotunda, so that the lower and middle parts of the structure must have arisen only after the corresponding levels of the drum had already been completed. Again, the three levels of the grottoni do not necessarily represent different building phases. The final section to be built was the portico, which is independent of the rotunda and cannot be any earlier than the upper levels of the intermediate block, which are essential prerequisites for its construction. Current arguments for a change in design affecting the portico also assume that this was added last.29
Practical constraints also affect the size of the workforce and the time taken for construction, the kind of logistical considerations that are still an essential part of modern building practice. The construction period is limited by the length of the building season and the number of days when no building work is taking place. A recently discovered series of grafitti from the near-contemporary Baths of Trajan has provided a unique window on the actual working conditions prevailing on major imperial building sites in Rome.30 The sequence of dates painted roughly on the walls of the structure as it rose suggest that there were no rest days, and that the builders worked from at least late February to October. If we apply this work schedule, but allow for the constraints on construction due to adverse weather conditions in the winter months, then we can assume a construction season of 270 days over 9 months for outdoor work, with indoor work (some materials preparation, interior decoration) continuing over a 12-month season of 365 working days maximum.
The main logistical constraint on the speed of construction is the maximum number of men that can be assigned to any given task. The most important of these is the maximum number of masons that can be employed simultaneously along any given stretch of wall or foundation, which is largely determined by the physical geometry of the structure. While the Renaissance architect Filarete recommended a minimum spacing of masons of 1.85 meters, the average span of an adult male, the pattern of the grafitti from the complex semicircular exhedra of the Baths of Trajan implies a spacing of 3.5 meters, roughly twice that;31 given the much larger diameter and the fewer reentrant elements such as niches in the Pantheon, for this exercise a slightly closer spacing of 3 meters will be assumed. It would therefore not be feasible to fit more than about 100 masons working on the brick facings and core at the same time on any level of the rotunda, which suggests a minimum time for each of the first three levels of about 260 days; the external cornices of the rotunda therefore might each have represented the end of a single building season.32 In comparison, no stage of the intermediate block or the grottoni would need anything more than half a season; indeed, it would be theoretically possible to have built the middle or upper zone of the intermediate block, or the lower or middle zone of the grottoni, in less than 100 days each. The shortest possible theoretical schedule for the Pantheon would, therefore, be six years, assigning a year each to the site works, foundations and substructures; the lower zone of the rotunda and intermediate block; the middle zone of the rotunda and the foundations of the grottoni; the upper zone of the rotunda and all of the grottoni; the completion of the dome, the rest of the intermediate block and the portico; and the decoration. As Lise Hetland’s redating of the Pantheon based on the brickstamps33 provides a starting date of AD 112–114, this six-year schedule would suggest a possible completion date of AD 117–119.
The presence of dated brickstamps in the fabric of the Pantheon, however, enables us to refine this schedule and makes such an early completion date unlikely. The catalogue published by Bloch provides sufficient information to locate about 50 stamps with a reasonable degree of certainty.34 The stamped bricks are not distributed uniformly, but it is significant that stamps of Rutilius Lupus with secure consular dates of AD 114 and 115 occur in the middle zone of the rotunda, and those of AD 117 in the upper level of the grottoni, built together with the upper zone of the rotunda. This makes it certain that the dome itself must have been completed under Hadrian, but the total absence of clearly Hadrianic brickstamps, particularly those of AD 123, in the whole of the main fabric, including the dome and the upper part of the intermediate block, excludes a predominantly Hadrianic structure, as Hetland has also noted. On the other hand, studies of late Trajanic and Hadrianic structures at Ostia suggest that the majority of bricks tended to be used relatively soon after they were produced,35 so that it is reasonable to assume that work on the Pantheon had indeed begun by AD 114, rather than that these stamped bricks represent old stock. Assuming that the work could not begin before 112, and more likely 113, and allowing also for the construction pattern of the grottoni, which might have required a hiatus before work started on the upper zone of rotunda (see the section “Years 3–5: Completing the Rotunda and the Grottoni”), a minimum construction schedule over seven years, plus two for decoration, ending in AD 122, would be feasible. This proposed schedule could equally be spread over more years if there were any unforeseen breaks in construction, for example due to structural problems or delays in the supply of materials,36 but the absence of stamps of AD 123, except for one possible example behind the decoration in the porch, does not allow the schedule to be extended beyond a couple of years, finishing with the decoration in AD 123 or 125. This schedule provides a strong working hypothesis that can be used to assess the size of the workforce.
The Size of the Workforce
Calculating the size of the required workforce involves further assumptions, and can only produce average minimum figures. It is assumed that all of the labor works at full capacity for the whole of 10 hours per day, and that the required workforce is always available – neither being very likely if modern practice is any guide. It is also assumed that Roman contractors avoided extreme peaks in labor demands as far as possible, as happens in modern construction projects where they are considered weak points in the scheduling. This would have been particularly important where skilled workmen were concerned, for example, the marble workers preparing the stone for the orders. Such calculations and considerations are of course hypothetical, and many other sche
dules are possible, but the exercise at least allows us to establish some realistic minimum parameters for the work. The suggested figures are given in Table 6.5.
Table 6.5. Number of men required for a 9-year construction schedule
* * *
YearDaysPorticoIntermediate blockRotundaGrottoniTotal
1 135 Groundworks ?
135 Foundations 10 Foundations 20 Foundations 170 200
2 340 Prepare orders 60 60
255 Lower level 40 Lower zone 190 230
15 Erect orders 100 100
3 40 Prepare cornice 60 60
80 Middle zone 230 230
20 Foundations 70 70
170 Lower and middle levels 135 135
4 160 Middle zone 230 Start bridge 10 240
15 Erect cornice 50 50
95 Start upper zone 230 Continue bridge 10 240
5 340 Prepare stone 60 60
270 Complete upper zone 230 Complete bridge 10 240
6 340 Prepare stone 60 60
270 Middle level 40 Dome to coffers 200 240
7 120 Upper level 50 Complete dome 90 140
130 Erect 50 50
8–9 Finish decoration Finish decoration Finish decoration ?
* * *
Year 1: Foundations and Site Preparation
If we assume that the making of the foundations for the portico, rotunda, and intermediate block occupied all of the first season of 270 days, only a relatively small number of men – roughly 100 – would have been required. The shortest possible time, determined by the maximum number of men who could work on the rotunda foundations at any time, would be about 90 days, needing 300 men each day. Neither of these figures, however, takes into account any of the preparatory groundworks, which could have occupied, say, half of the first season. In Table 6.5 it has, therefore, been assumed that the digging and laying of the foundations occupied only the second half of the season, that is, 135 days, requiring an average workforce of about 200 men each day, who might have spent the same sort of time in the preliminary groundworks.