Pompeii was built about above sea level on a coastal lava plateau created by earlier eruptions of Mount Vesuvius, ( distant). The plateau fell steeply to the south and partly the west and into the sea. Three sheets of sediment from large landslides lie on top of the lava, perhaps triggered by extended rainfall. The city bordered the coastline, though today it is away. The mouth of the navigable Sarno River, adjacent to the city, was protected by lagoons and served early Greek and Phoenician sailors as a safe haven and port which was developed further by the Romans.