Northeast of the "forum", in Via della Rotonda, a circular building covered with a dome supported by eight arches constitutes the only remaining part of an interesting thermal complex. 

In the sixth century the structure was transformed into a Christian church, raising the floor level by some two meters. Of the niches for the bathing pools, one was used for the apse, the other two for lateral chapels. 

Despite this transformation, the building was correctly identified by the Prince of Biscari. Excavations and restorations carried out in the early 1950s by Guido Libertini brought to light two phases in the use of the complex: the earliest late Hellenistic, the most recent in the imperial age (second-third century AD).