It is the most important town in the valley upstream from Senigallia, lying 14 kilometres (9 mi) from the Adriatic coast.

Pliny the Elder mentions Ostra with another ancient town, Suasa, 8 kilometres (5 mi) west.

Though Ostra is little mentioned by ancient authors, excavations there have brought to light remains of various buildings and several inscriptions.

Here also are the town hall with its arches and its marble staircase and St Francis' Church, built in the 13th century.

Built in the late Middle Ages, the wall surrounding the town is perfectly preserved for a total length of 1,200 metres (3,900 ft).