La copertura dell’aula Giulio Cesare nel Palazzo Senatorio in Campidoglio. Note sul cantiere di fine Ottocento

In 2009, the bolt connecting the metal tie-beam to the timber rafter of one of the 11 composite Polonceau trusses mounted in the main body of the Senatorial Palace in Campidoglio square – now the town hall of Rome – unexpectedly broke. The need to repair the great roof – which lies directly above Julius Caesar’s Hall – gave rise to a study which was to prepare the way for a project. This paper presents the results of the preliminary fact-finding analysis of that project. The analysis particularly focused on the nineteenth-century alterations that were made to the great vaulted ceiling of Julius Caesar’s Hall and the double-pitched timber roof above. These alterations date back to June 1893, when the collapse of portions of plaster from the intrados of the hall’s barrel vault triggered a process that – on the construction site set up to replace the great masonry vault with a metal one of the same shape – would lead to the decision to dismantle the sixteenth-century timber trusses as well, replacing them with composite Polonceau trusses. The comparison between archive data – particularly the visuals documenting the late nineteenth-century project – and the current situation, surveyed on site, allowed us to identify with enormous precision the substitutions that were carried out on the main structures – the vault and the roof – as well as associated work undertaken on masonry in order to create the structures that would support the new additions.