Ostia Antica is a large archeological site, close to the modern suburb of Ostia, that was the location of the harbour city of ancient Rome, which is approximately 30 kilometres (19 miles) to the northeast. "Ostia" (plur. of "ostium") is a derivation of "os", the Latin word for "mouth". At the mouth of the River Tiber, Ostia was Rome's seaport, but due to silting the site now lies 3 kilometres (2 miles) from the sea. The site is noted for the excellent preservation of its ancient buildings, magnificent frescoes and impressive mosaics.