Bacău (UKˈbækaʊ , USbəˈkaʊ , baˈkəw; Bákó; Bacovia) is the main city in Bacău County, Romania. With a population of 136,087 (as of 2021 census), Bacău is the 14th largest city in Romania. The city is situated in the historical region of Moldavia, at the foothills of the Carpathian Mountains, and on the Bistrița River (which meets the Siret River about to the south of Bacău). The Ghimeș Pass links Bacău to the region of Transylvania.
The town's name, which features in Old Church Slavonic documents as Bako, Bakova or Bakovia, comes most probably from a personal name. Men bearing the name Bakó or Bako are documented in medieval Transylvania and in 15th-century Bulgaria, but according to Victor Spinei the name itself is of Turkic most probably of Cuman or Pecheneg origin. Nicolae Iorga believes that the city's name is of Hungarian origin (as Adjud and Sascut). Another theory suggests that the town's name has a Slavic origin, pointing to the Proto-Slavic word byk, meaning "ox" or "bull", the region being very suitable for raising cattle; the term, rendered into Romanian alphabet as bâc, was probably the origin of Bâcău. In German it is known as Bakau, in Hungarian as Bákó and in Turkish as Baka.
Similarly to most urban centers in Moldavia, Bacău emerged on a ford that allowed water passage. There is archaeological evidence of human settlement in the centre of Bacău (near Curtea Domnească) dating from the 6th and the 7th centuries; these settlements were placed over older settlements from the 4th and the 5th centuries. A number of vessels found here are ornamented with crosses, hinting that the inhabitants were Christians. Pechenegs and Cumans controlled the Bistrița valley during the 10th, 11th and 12th centuries. Colonists played a significant role in the development of the town. Archaeological finds, some surface or semi-buried dwellings from the second half of the 15th century, suggest that Hungarians started to settle in the region after 1345–1347 when the territory was under the control of the Kingdom of Hungary.