Founded by Grand Chancellor Matteo D’Ajello, this church was first entrusted to the Cistercians, who, in 1197, were obliged by Henry VI to hand it over to the Teutonic Knights. It is a single-volume basilica, the transept without arms. The three apses, in line with the nave and aisles, merge with the transept, as in other churches of the period. At its centre are four large cruciform piers linked by wide pointed arches, (the square-shaped superstructure does not carry a dome). The piers of the transept are less massive, as the residual thrust from the great central arches is transmitted to two terminal buttresses located between the apses. These structural features are evident in the external design of the building, creating a balanced interplay of square and prismatic volumes. The first part of the main basilica is divided into three by columns carrying pointed arches. This church is a splendid example of late 12th-century Siculo-Norman structural design.
Guido Di Stefano, "Monumenti della Sicilia Normanna", Palermo, 1979
Melo Minnella Palermo