Greek colonists founded Pozzuoli in the 7th century BC and under the Roman domination it grew to be the most important port in the Western Mediterranean. The city's history is linked to a phenomenon that causes the Earth's crust to rise and fall with respect to the level of the sea. A sign of this phenomenon can be seen in the Temple of Serapis, the ancient Roman market which is periodically submerged under the waters. Other evidence of the city's rich and important past can be seen in the Anfiteatro Flavio in the higher part of the city, the Neptune thermal complex, the numerous churches, Villa Avellino and the famous Solfatara volcano.