Ostia is the coastal hamlet that is part of the municipality of Rome Capitale: a well-known tourist location, it overlooks the Tyrrhenian Sea near the mouth of the Tiber river. Much of the area was built starting from the early years of the 20th century, after the reclamation of the area which took place following the annexation of Rome to the Kingdom of Italy. According to tradition, it was the king of Rome Ancus Marzio who founded Ostia in 620 BC. to exploit the salt pans at the mouth of the Tiber. The oldest remains known so far, however, are later, that is, from the second half of the 4th century BC: they are the ruins of a fortified structure (castrum) made of tuff blocks, built by Roman colonists to defend the mouth of the Tiber and the Lazio coast. The archaeological park of Ostia antica, in which the remains of the ancient Roman city of Ostia are preserved, represents a site of great archaeological interest in constant development and updating. The places of greatest interest are the Decumanus Maximus, the baths of Neptune – where a spectacular mosaic of the god on a chariot pulled by four horses is preserved -, the Necropolis with tombs from the 2nd century BC, the baths of the Seven Wise Men, the public latrines and the Roman theatre. Near the Park, stands the medieval village of Ostia Antica with the castle of Julius II: the village developed following the abandonment of the ancient Roman city of Ostia. In Ostia, the civil architecture is numerous and largely dates back to the 1920s. There are also numerous churches, urban parks and natural areas.