Piazza Unità d'Italia (Unity of Italy Square in English) is the main square in Trieste, a seaport city in northeast Italy. Located at the foot of the hill with the castle of San Giusto, the square faces the Adriatic Sea. It is often said to be Europe's largest square located next to the sea. The square was built during the period when Trieste was the most important seaport of the Austrian-Hungarian Empire and includes the city's municipal buildings and other important palaces.