Restoration of the Zisa Palace, Palermo

The building of the Zisa, commissioned by William I, began in 1164-1165; it was completed by William II in the years immediately following. It was built as a splendid place for rest and amusement, the royal sollatium. Still today, despite violations it has undergone in the course of time, it is one of the most important examples of Arab-Norman architecture. It is worth pointing out that the collapse occurred in line with the big staircase constructed in the 17th century, which jeopardised the resistance of the overall structural complex. The Zisa being in a secondary category seismic zone, the designers believed they should also consider its structural behaviour towards dynamic excitations. The solution adopted was to cage the whole structural complex with a system of pre-stretched cables running vertically and horizontally inside the walls, and welded with the masonry by means of cement mortar injections.