The rift valley remained a depression in the Tyrrhenian Sea for about 2 million years and then in the Tuscolano-Artemisio phase, dated 600-360 thousand years BP, a series of volcanic changes began leading to the current land form: the first four eruptive cycles of a new volcano in the vicinity of the Monti Albani, which spread pyroclastic rock and formed a caldera. In the Campi di Annibale phase, 300-200 thousand years BP, a stratovolcano formed in the caldera. Approximately contemporaneously, in the Middle Pleistocene, 781-126 thousand years BP, beds of sand and clay, termed the Latina Complex, appeared above sea level over the outer karst, enclosing a lagoon. The beaches survive as the Latina Level from about 560 thousand years BP.