A small but worthwhile museum in a 17th-century mansion across the square from the Théâtre Antique. The star exhibit is the Roman cadaster of Orange — a set of carved marble panels found in 1949 that map the agricultural parcelling of the Orange region in the first century AD. They are the most complete Roman land registry to survive anywhere and remain a key source on Roman land management.
Other galleries cover the medieval and Renaissance principality of Orange (held by the House of Nassau, ancestors of the Dutch royal family), and a small collection of paintings including works by the local Provençal school. A combined ticket includes the theatre across the square.