Churches and places of worship Cattedrale di San Pietro Apostolo The Cathedral of St. Peter the Apostle was built in the historic center of Isernia and stands on an ancient temple of the 3rd century BC. Its appearance has seen changes over the centuries mainly due to the earthquakes occurred and renovations carried out later. The outer part is composed of a large triangular gable. The structure is supported by four ionic columns and two pairs of pillars at the corners. The interior space is divided into three naves consisting of four spans each.