It is not known when Bolu was first established. Some archaeological findings that date back about 100,000 years suggest the region was inhabited then. The area now in Bolu Province was in eastern
Bithynia and southwestern
Paphlagonia. The town of Bithynium, from which the area takes its name, is the modern
Bolu. The area was called Bithynia during the
Hellenistic period. The
Romans named it Claudiopolis, and it was called Bolu by the Turks. 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. The Bithynian region, with parts of Paphlagonia remained its own kingdom until 88 BCE, when it briefly came under
Mithridates VI and the
Kingdom of Pontus. With Roman's help, the last Bithynian king,
Nicomedes IV, regained his throne, but on his death bequeathed the kingdom to Rome. 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. Under the falling
Byzantine Empire, the Bolu area was divided from western Bithynia at the
Sakarya River, with western Bithynia keeping the name. The Sakarya River remains the southern and western boundary of the province. After the victory of
Malazgirt in 1071, the Turkmens spread to the west and settled in Bolu 3 years later. The Turkmens who settled in
Bolu in 1074 easily integrated with the
Bulgar,
Pecheneg,
Uz and
Cuman Turks that the
Byzantine Empire's had brought from the
Balkans long before and later. Bolu and its villages were completely Turkified and took the names of the
Turkic tribes. The
Turks who came from the Balkans became
Christians, but they did not forget the
Turkic language, customs and traditions. They became
Muslims in a short time. 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. After the end of the
Komnenos dynasty, the Turks gradually reclaimed the Bolu area back. In approximately 1240, the Seljuk Turks took the eastern part of the Bolu area (i.e., the Paphlagonian part) from the Byzantine Empire and incorporated it into the
Sultanate of Rum. 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. That eastern area fell to the
Isfendiyarids in 1292 and was controlled by them until 1461, after which it was incorporated into the rest of the
Ottoman Empire by
Mehmed II. 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. The two areas were reunited in 1461, under Mehmed II. In the
1864 Ottoman Empire administrative reorganization, Bolu was made into an independent
sanjak, although it was geographically part of the
Kastamonu Vilayet. ==Administrative divisions==