Ancient Histria or Istros (Ιστριη, Thracian river god, Danube), was a Greek colony or polis (πολις, city) on the Black Sea coast, established by Milesian settlers to trade with the native Getae. It became the first Greek town on the present day Romanian territory. Scymnus of Chios (ca 110 BC), the Greek geographer and poet, dated it to 630 BC. Eusebius of Caesarea, some centuries later, dated its founding to 657 – 656 BC, at the time of the 33rd Olympic Games. The earliest documented currency on Romanian territory was an 8-gram silver drachma, issued in Histria in the year 480 BC.

Archaeological evidence seems to confirm that all trade with the interior followed the foundation of Histria. Traders reached the interior via Histria and the Danube valley, demonstrated by finds of Attic black-figure pottery, coins, ornamental objects, an Ionian lebes and many fragments of amphoras. Amphoras have been found in great quantity at Histria, some imported but some local. Local pottery was produced following establishment of the colony and certainly before mid-6th century. During the archaic and classical periods, when Histria flourished, it was situated near fertile arable land. It served as a port of trade soon after its establishment, with fishing and agriculture as additional sources of income. By 100 AD, however, fishing was almost the sole remaining source of Istrian revenue.

Around 30 AD, Histria became a Roman town. During the Roman period from the 1st to 3rd centuries AD, temples were built for the Roman gods, besides a public bath and houses for the wealthy. Altogether, it was in continuous existence for some 14 centuries, starting with the Greek period up to the Roman-Byzantine period. The Halmyris bay where was the city founded was closed by sand deposits and access to the Black Sea gradually was cut. Trade continued until the 6th century AD. The invasion of the Avars and the Slavs in the 7th century AD almost entirely destroyed the fortress, and the Istrians dispersed; the name and the city disappeared.

Ancient Histria was situated on a peninsula, about 5 km east of the modern Romanian commune of Istria, on the Dobruja coast. The ancient seashore has since been transformed into the western shore of Sinoe Lake, as the Danube's silt deposits formed a shoal which closed off the ancient coastline. The current Sinoe Lake was at the time the open northern bay, while another bay on the southern shore served as the port. The acropolis with sanctuaries was established on the highest point of the coastal plain. The settlement itself, erected in the 6th century, was 800 m to the west of the acropolis. The settlement had stone paved streets and was protected by strong wall. Water was collected along 20 km long aqueducts. The ruins of the settlement were first identified in 1868 by French archaeologist Ernest Desjardins. Archaeological excavations were started by Vasile Pârvan in 1914, and continued after his death in 1927 by teams of archaeologists led successively by Scarlat and Marcelle Lambrino (1928–1943), Emil Condurachi (1949–1970), Dionisie Pippidi, Petre Alexandrescu and Alexandru Suceveanu. The Histria Museum, founded in 1982, exhibits some of these finds. The excavation project and site also features prominently in the film The Ister.