The Restoration of Diocletian's Palace – Mausoleum, Temple, and Porta Aurea (with the analysis of the original architectural design)

Abstract

During the restoration of the Cathedral in 1996, new evidence was found to create a clear picture of the original shape of the Mausoleum’ s roof and of the reasons for its thorough remodelling in the 13th century. Because the interior and exterior elevations of the Mausoleum were designed separately (although in the similar proportional system), it happened that the dome was made too high above the upper cornice of the facades. The pitch of the roof was too steep and over the centuries the tiles were sliding down. In the thirteenth century, at the time of the great reconstruction of the interior of the Cathedral and at the start of the construction of the bell-tower, the form of the roof was changed. The pitch of the roof was lowered, an attic wall was built above the Roman cornice, and a finnial was put on the top. The roof was then covered with Roman tiles collected from the Mausoleum itself and from ruined buildings within Diocletian's palace. During the recent restoration, over 500 Roman tegulae were found on the roof, were repaired and kept in place. Roman builders made a similar mistake in the Temple of Jupiter. Again, the exterior cornice was made too low in respect of the vault, so there was not enough space between the extrados of the vault and the contour of the pediment for a normal timber roof structure. Only the roof over the pronaos (which disappeared a long time ago) was erected, and preparations were started to provide for the fixing of a makeshift roof structure over the vault. However, that part of the roof was never made, very probably because the Emperor came to live in his new palace earlier than had been planned. Not only the roof, but also a great part of architectural decoration of the Temple was left unfinished for the same reason. (The same applies to the Mausoleum and the Porta Aurea.) Material evidence to support this reasoning was found on the building during the structural consolidation works in 2002, when the west gable was dismantled. Restoration work on the Porta Aurea of Diocletian Palace has just started. Conservation problems are very complicated, and particularly those connected with the structural safety of the north wall. Some of those problems are rooted in the mistakes committed during the designing and building of the Gate. It seems that changes were introduced in the original design, due to bad co-ordination of the interior and exterior levels of the ground, and of the lateral towers, which were finished before the Gate itself. Furthermore, the original design of the facade did not take into account the slot in the wall where the portcullis had to be accommodated. For that reason one of the niches was made too shallow to receive a statue, and the wall was weakened. The stability of the wall was further hampered when a medieval vault was constructed over the guard’ s passage which was converted into a church. Following the dismantling of the columns (probably in the late 18th century), the arches on top of the facade became cantilevered, and the whole upper half of the wall is now leaning outward.