oasis in Maṭrūḥ muḥāfaẓah (governorate), western Egypt. It lies near the Libyan frontier, 350 miles (560 km) west-southwest of Cairo. The oasis is 6 miles (10 km) long by 4–5 miles (6–8 km) wide and has about 200 springs. Two rock outcrops provide the sites of the old walled settlements of Siwa and Aghūrmī, which are veritable fortresses. The oasis is inhabited by Berber-speaking Sudanic peoples who live in mud-brick houses at the foot of their former strongholds. Ten miles (16 km) northeast is the small oasis of Az-Zaytūn (Zeitun), and westward a chain of little oases and small salty pools extends for about 50 miles (80 km). Siwa Oasis is extremely fertile and supports thousands of date palms and olive trees. The export of dates and olive oil provide the chief source of income, supplemented by basketry.

Siwa's ancient Egyptian name was Sekht-am, meaning “palm land.” The oasis was the seat of the oracle temple of Amon (Zeus Ammon), which was already famous in the time of Herodotus and was consulted by Alexander the Great. The fragmentary remains of the temple, with inscriptions dating from the 4th century BC, lie in the ruins of Aghūrmī. The oracle fell into disrepute during the Roman occupation of Egypt. Nearby is the ruined temple of Umm Beda (Um Ebeida), and there are also many Roman remains in the vicinity. The first European to reach Siwa after Roman times was the British traveler William George Browne in 1792.