Mainz Citadel’s main gate bends on purpose. A cannonball would hit a thick stone wall, and anyone who broke in could be attacked from the sides rather than head-on.

The hill was a Roman base long before, with up to 12,000 soldiers. By around the year 1000 a Benedictine abbey stood here, and in the 1600s the fortress swallowed its buildings. Elector Johann Philipp von Schönborn built the citadel, and the baroque gate, from around 1660, still carries a figure of St James for the monastery inside. Salvaged monastic stonework turns up elsewhere, from a doorway beside the commandant’s house to the scalloped window frames of a 1914 barracks.

VoiceMap’s Roman Legacy tour walks you through the bent gate, sorts the Roman, monastic and military layers, and passes the bomb-proof garrison with its dry moat.