Athens sprawls across the central plain of Attica that is often referred to as the '''Athens Basin''' or the '''Attica Basin''' (). The basin is bounded by four large mountains: Mount Aigaleo to the west, Mount Parnitha to the north, Mount Pentelicus to the northeast and Mount Hymettus to the east. Beyond Mount Aegaleo lies the Thriasian plain, which forms an extension of the central plain to the west. The Saronic Gulf lies to the southwest. Mount Parnitha is the tallest of the four mountains (), and has been declared a national park. The Athens urban area spreads over 50 kilometres (31 mi) from Agios Stefanos in the north to Varkiza in the south. The city is located in the north temperate zone, 38 degrees north of the equator.