Just above Trg Ivana Koblera is a massive and plain stone archway, the oldest structure in Rijeka, once the entry into the Roman Praetorium, the military command centre. Built onto it is an odd structure: half-church, half socialist department store, with a Hapsburg era town house added on for good measure. Go through the arch and you come to Roman excavations where you can see decorative columns, stone walls and slabs.