The oldest archaeological evidence attested in the territory of Osimo comes from the lower valley of the
Musone river and its right tributary
Fiumicello, which date back to the
Upper Paleolithic (40,000-12,000 years ago). In the 9th century BC, the
Picentes settled on the hill of Osimo and on the peak of Monte San Pietro, giving life to two distinct settlements with relative
necropolises. With the
Battle of Sentinum (today
Sassoferrato) in 295 BC, the
Romans began the conquest of
Picenum region, which involved Osimo starting from 173 BC. Vetus Auximum – the ancient Osimo – was founded by the ancient Romans, who used it as a fortress for their settlement in northern
Picenum. The walls were made of large rectangular stones which are still visible in some locations. It became a Roman colony in 157 BC. The family of
Pompey were its protectors and resisted
Julius Caesar in 49 BCE. Inscriptions and monuments in its town square attest to the importance of Osimo during imperial times. In the 6th century it was besieged twice in the course of the
Gothic War (535–554) by
Belisarius (see
siege of Auximus) and
Totila; the
Byzantine historian
Procopius said it was the leading town of Picenum. Osimo was a free commune by 1100 A.D. It was later returned to the Pope by Cardinal
Gil de Albornoz. In 1399–1430, it was a fief of the
Malatesta family, who built a
rocca, or "castle", which is no longer intact. Osimo was again made a part of the
Papal States, and remained so until
Italian unification in 1861. ==Main sights==