Remains from the first church, possibly from the reign of Constantine I, and earlier Roman houses can be seen in the lower parts, reached by a staircase in the sacristy. The ruins are confusing, but you can easily find the apse of the old church and you can see the remains of the martyr's shrine in middle of the apse wall. The church had an uncommon form; rather than the normal basilical plan with a central nave and two aisles on the sides, it had a single nave.