4. Damage areas in the Macellum

4.1 Overview of the building

Figure 4.1 shows a plan of the Forum, with the Macellum highlighted in the upper right corner; figure 4.2 shows a plan of the building.

Figure 4.1: A plan of the Pompeii Forum, with the Macellum highlighted in the upper right.

Figure 4.2: A plan of the Macellum [Dobbins 1994]. Reference north is upward.

The plan uses the numbering system developed by Dobbins [1994, p. 636], where numbers are assigned to spaces, and walls are identified using the numbers they separate: W7.8 refers to the wall separating spaces 7 and 8, with particular attention on the surface facing space 7.

To document the patterns of damage in three dimensions, this study has developed a three dimensional model of the Macellum, which includes the following components:

• Photogrammetric models: These are models of portions of the building created with digital photogrammetry software. Appendix A outlines these models and their source photographs.
• Extruded Model: This is a simple model of the Macellum walls developed by extruding the plan of the building. The height of the extrusion is an estimate of 6 meters, based on the heights of currently visible second-floor beam pockets.
• Ground Form: Although the Macellum is graded nearly level in its interior, the exterior ground slopes downward to the east and south. The model includes a three dimensional base approximating this grading, and also includes foundation trenches where the walls penetrate the earth.

Appendix B describes the extruded model and ground form model in more detail. Figure 4.3 shows the model with all its components visible, rendering the extruded plan as a wire frame. Figure 4.4 shows the ground form model alone.

Figure 4.3: Overall view, with all photomapped models, ground plane, and extruded model, viewed from the south east

Figure 4.4: Three dimensional model of the ground form.

The damage areas typically encompass areas larger than can be designated by a single identifier with the Dobbins numbering system, so an additional identification system is used, labelling the five areas of apparent out-of-plane failure with the letters A through E, shown highlighted in figure 4.5, which views the building from the south. Figure 4.6. shows a photograph of the south face of each area.

Figure 4.5: Overall view with photo-mapped models of key damage areas, viewed from the south.

Area A	Area B	Area C	Area D	Area E

Figure 4.6: Thumbnail photographs of the five damage areas. All views show the south face of the wall.

4.2 Comparing with the Naples Museum Model

The computer models described above are not the first three-dimensional models of the Macellum. The National Archaeological Museum of Naples houses a model of the entire city, developed in the late 19th century, and many of the Forum buildings are rendered in remarkable detail. Comparing the rendition of the Macellum in the Naples model with the current state of the building gives some insights into its reconstruction.

Figure 4.7 shows the Naples model rendition of the Macellum, revealing a key difference relative to the current building: the Naples model shows relatively little variation in the height of the perimeter wall, in contrast to the current building, which includes abrupt and significant changes in height, particularly at the north wall.

Naples museum model (photo courtesy of Larry Ball)

Computer model

Figure 4.7: A comparison of the Naples Museum Model showing the state of the building in the late 19th century, and the computer model showing the current state.

The difference in wall profile implies that wall material has been added, removed, or both since the development of the Naples model. The evidence suggests the following scenario: The height of the north wall in the Naples model, seems to be much higher than the current wall in the area of the north gate. Figure 4.8 shows a view of the model from the northwest, compared to a view of the computer model, focussing on the north gate.

Naples museum model (photo courtesy of Larry Ball)

Computer model

Figure 4.8:A comparison of the north perimeter wall near the north gate. Note the much lower height in the modern model.

Compared to the current state of the walls, the Naples model shows that the portions of the perimeter wall flanking the north gate are much taller than the adjoining shop walls, so that the upper portion of the perimeter wall has no intersecting walls to buttress it, making it very vulnerable to out of plane failure; it's credible that even a small earthquake could have toppled the upper portion of that unsupported wall. Possible events to cause this damage are the earthquakes of 1857, 1930, and 1980 (see chapter 2). Of these, it is unlikely that it ocurred in 1980, because documentation of that earthquake reports no such damage [Triches 1982]. Determining whether the 1857 or 1930 earthquake was the cause of the damage requires archival information concerning the process of creating the Naples model, and this study has not yet acquired that information.

In either case, it is likely that a minor post-excavation earthquake induced damage that toppled the upper portion of the north perimeter wall, particularly in the regions flanking the north gate. The repair involved finishing off the perimeter wall near the gate at a lower height, only slightly taller than the shop walls flanking the gate. Figure 4.9 shows the interior of shop 7 immediately east of the gate, the coarse masonry work at the top of the perimeter wall was probably part of the process of leveling the wall after the post-excavation earthquake.

Figure 4.9:The interior of shop 7. The coarse masonry work at the top of the main wall is probably leveling of modern earthquake damage.

In addition to lowering the perimeter wall at the gate, this modern repair also apparently raised the wall at the northwest corner. Figure 4.10 below clearly shows that the tall portion of the wall is a different construction from the material directly below it.

Figure 4.10:The juncture of the high and low portions of the perimeter wall at the northwest corner. The upper part of the wall is clearly a different construction.

Looking under the roof that has been placed over the northwest corner, the ancient frescos clearly indicate ancient fabric. Figure 4.11 shows the interior of the corner, with the west wall on the left.

Figure 4.9:The interior of the northwest corner (now roofed). The frescoes are clearly part of the ancient fabric.

The top of the frescos on the west wall probably indicate the top of the wall as depicted in the Naples model. At the time the Naples model was developed, the north wall probably matched this height. The drop in the top of the fresco at the north wall is probably the result of modern earthquake damage, and the out-of-plane failure of the upper portion of the north wall. Therefore, the abrupt change in height at the west end of the north wall is the result of a combined lowering of the height near the gate and raising of the height near the corner, probably both in response to damage from a modern earthquake, in either 1857 or 1930.

4.3 Summary

The Macellum includes five areas that show the characteristic scooping profile of out-of-plane masonry failure, which are the result of either seismic shaking in 62 or in 79. As discussed in chapter 3, it is unlikely that the damage in these areas is the result of pyroclastic flow. In addition, comparison of the current state of the building with the Pomepii model at the The National Archaeological Museum of Naples reveals that the building has suffered some earthquake damage since its excavation, resulting in a reduction in the height of the north perimeter wall near the north gate.

Concerning the post-62 reconstruction of the building, the key question for each of the five damage area is whether the repair is ancient or modern. One of steps in pursuing this question involves comparative analysis of the five areas, explaining similarities and differences among them based on their structural conditions and relative vulnerability to damage. The next chapter examines the characteristics that influence the vulnerability of the Macellum walls to damage.