To the west of Eleusis, the Greek mainland narrows into Megaris, connecting to the Peloponnese at the Isthmus of Corinth. The western coast of Attica, also known as the Athens Riviera, forms the eastern coastline of the Saronic Gulf. Mountains separate the peninsula into the plains of Pedias, Mesogeia, and the Thriasian Plain. The mountains of Attica are the Hymettus, the eastern portion of the Geraneia, Parnitha (the highest mountain of Attica), Aigaleo and Penteli. Four mountains—Aigaleo, Parnitha, Penteli and Hymettus (clockwise from the southwest)—delineate the hilly plain on which the Athens urban area now spreads. Mesogeia lies to the east of Mount Hymettus and is bound to the north by the foothills of Mount Penteli, to the east by the Euboean Gulf and Mount Myrrhinous, and to the south by the mountains of Lavrio (modern Lavreotiki), Panio (Πάνειο Όρος), and Laureotic Olympus (Λαυρεωτικός Όλυμπος). The Lavrio region terminates in Cape Sounion, forming the southeastern tip of the Attic peninsula.