Viareggio (Italian pronunciation: [vi.aˈreddʒo; vjaˈreddʒo]) is a city and comune in northern Tuscany, Italy, on the coast of the Tyrrhenian Sea. With a population of over 64,000, it is the second largest city within the province of Lucca, after only Lucca city. The city traces its roots back to the first half of the 16th century when it became the only gate to the sea for the Republic of Lucca. The oldest building in Viareggio, known as Torre Matilde, dates back to this time and was built by the Lucchesi in 1541 as a defensive fortification to fight the constant menace of corsair incursions.