Intersected by roads which used to cross the Valleys of Siret, Bistriţa and Trotuş, the county of Bacău was the cradle of human activity early in its history, and that is proved by numerous archeological discoveries. In the age of Roman rule over some areas of Dacia, the civilization of Carpi or Carpiani inhabited the territory of the County of Bacău and other areas; in the second and third centuries they created an interesting civilization. The research carried out at Măgura, Bărboasa, Cârligi, Sohodol, Săuceşti has contributed to the knowledge of the history of this civilization, which developed in the wake of the Geto-Dacian civilization. History proves the continuity of the local population in the next centuries, as well as the inclusion of these regions in the area where the Romanian people was born and flourished.
The evolution of the developing stage of feudalism east of the Carpathians resulted in the appearance of hamlets. A document issued at the chancellery of Prince Alexander the Good on the 6th of October 1408 makes reference to the hamlets of Bacău and Trotuş.
The foundation of the settlement is even older. While diggings were under way, 12th and 14th century pottery and coins issued during the reign of Petru Muşat (1375-1391) were discovered in the city of Bacău.
Due to the privileges granted by the ruler to the foreign mechants, the City of Bacău made fast progress. In the 15th century it had become an important centre for trade and craftsmanship, where customs transactions were done, and where a judicial authority and execution bodies operated.
At present Bacău covers an area of 6621 square kilometers, it includes 3 cities, 5 towns and 85 villages, with a population of more than 583.6 thousand inhabitants.