The Western Desert, is about 390 kilometres (240 mi) wide, from Mersa Matruh in Egypt to Gazala on the Libyan coast, along the Via Balbia, the only paved road. The Great Sand Sea 150 miles (240 km) inland marks the southern limit of the desert at its widest points at Jaghbub (Giarabub) and Siwa Oasis; in British parlance, Western Desert came to include eastern Cyrenaica in Libya. From the coast, extending 120–190 miles (200–300 km) inland, there is a flat plain of stony desert, about 500 feet (150 m) above sea level, until it meets the Sand Sea.