Austrian ruins previously known as the Desolate Castle were actually once a Roman bridgehead fort. Archaeologists solved the mystery of the ruins of the Desolate Castle, determining that the mysterious site on the Danube River shore was once part of a crucial Roman trade route. The site is Austria’s only known Roman bridgehead fort. Roman military strategy commonly called for the construction of forts on the opposite side of a border river. Related Story Archaeologists Found a Burned Roman SettlementThe Danube River was an important location for Roman border security and control of trade routes.