[3] By approximately 375 BCE, Bithynia had gained its independence from Persia under Artaxerxes II, and King Bas subsequently defeated Alexander's attempt to take it.

This led to the Third Mithridatic War and the fall of Pontus, after which the area was incorporated into the Roman Empire as a single province, merging Paphlagonia with Bithynia.

[5] The Byzantine Empire briefly lost the Bolu area to the Seljuk Turks after the 1071 Battle of Manzikert but recovered it under Alexios I Komnenos.

Due to their assistance in taking it and Sinop, the Chobanids were given that territory and adjacent areas to the north and east to govern.

By 1265, the western part of the Bolu area was again acquired by the Seljuk Turks, but it fell to Orhan and the Ottoman Empire in the early to mid-1300s.

In the 1864 Ottoman Empire administrative reorganization, Bolu was made into an independent sanjak,[6] although it was geographically part of the Kastamonu Vilayet.