Basilica Cattedrale di San Giusto Martire (also known as Trieste Cathedral), dedicated to Saint Justus, is a Roman Catholic cathedral and the main church of Trieste, in northern Italy. It is the seat of the Bishop of Trieste.



In 1899, Pope Leo XIII granted it the status of a basilica minor.



The first religious edifice on the site was built in the 6th century on some Roman propylaea, using part of the existing structure. Perhaps the entrance to a monument, this was commonly known as the Capitoline Temple, as a pyramidal altar with the symbols of the Capitoline Triad (Jupiter, Juno and Minerva) had been found inside it.



Of the hall there remains part of the mosaic floor, integrated into the present-day floor, which contains markings of the outer walls of the early Christian building. Soon after it was opened for worship, the church was destroyed in the Lombard invasion.



Between the 9th and 11th centuries, two basilicas were erected on the ruins of the old church, the first dedicated to Our Lady of the Assumption and the second, the cathedral, to Saint Justus (San Giusto). The original design of the latter building was subsequently lengthened. In the 14th century the two basilicas were joined by means of the demolition of one nave of either basilica and the construction of a simple asymmetrical façade, dominated by a delicately worked Gothic rose window, as ornate as the new bell tower, using the Romanesque debris stones found on the site and friezes of arms.



The Cappella di San Carlo Borromeo (Chapel of Saint Charles Borromeo) serves as the burial chapel for the family of the Carlist claimants to the throne of Spain.