Battle of Koyunhisar: The Founding Victory of the Ottoman State

Battle of Koyunhisar, also known as the Battle of Bafeus, took place between July 18, 1302, and July 27, 1302, between the Byzantine Empire (Eastern Roman Empire) and the Ottoman Beylik (which was in its early stages as a beylik at that time).

The significance of the Battle of Koyunhisar lies in it being the first battle between the Byzantines and the Ottoman Beylik. Under the leadership of Osman Gazi, this battle, fought with full force, marked an important entry for the Ottoman Beylik onto the historical stage.

Before the Battle of Koyunhisar, after the passing of Ertuğrul Gazi, Osman Bey was elected as the leader of the Kayı tribe in 1289. Initially, Osman Bey remained under the influence of the Çobanoğlu Beylik, which was established around Kastamonu, and acted in accordance with it.

Following the dissolution of the Çobanoğlu Beylik in 1291, Osman Bey gradually began to strengthen his own authority and, in alliance with groups conducting raids against the Byzantines, moved forward. In 1281, the first battle of the Ottoman State, the Armenian-Bel Conflict, took place, and then Seljuk Sultan Keykubat sent a decree informing Osman Bey of the establishment of the Söğüt frontier principality.

After Seljuk Sultan III. Alaeddin Keykubat was taken hostage by the Ilkhanids, an authority vacuum emerged in Anatolia, and as a result, in 1299, Osman Bey declared the independence of his principality.

Osman Bey maintained good relations with other principalities in Anatolia and set his expansion policy towards Rome, meaning westward, designating Byzantium as the natural enemy. Important regions like İznik, Bursa, and İzmit were under the administration of Tekfurs, who were Byzantine governors. While being independent in internal affairs, Tekfurs paid an annual tax to the Byzantines. Meanwhile, Byzantium, or the Eastern Roman Empire, was dealing with its own internal conflicts and couldn't pay much attention to the territories in Anatolia. Taking advantage of these troubles, Osman Bey seized important places like Yarhisar, Karacahisar, and Yenişehir from the Tekfurs, then turned his attention to İznik.

The reason for the Battle of Koyunhisar was the siege of İznik by the Turks. As Osman Gazi intensified his siege of the city, the occupied city couldn't receive supplies from the Byzantines. Osman Gazi also secured the communication and trade routes, cutting off potential reinforcements to the city. The regional Tekfurs united and sought help from Byzantine Emperor Michael IX Palaiologos. İznik was a crucial center for both the Ottoman and Byzantine sides.

Emperor Palaiologos realized that with the increasing strength of the Turks, capturing such an important center as İznik would further empower them. He understood that protecting İznik was essential to prevent a potential new Turkish attack.

Osman Gazi, with all his might, besieged İznik to the extent that the occupied city couldn't be resupplied by the Byzantines. He also controlled the connections and trade routes, blocking any potential aid to the city. Palaiologos, combining his paid troops with the forces of the Tekfurs of Bursa and Kestel, sent them on ships towards the shores of Yalova. The Byzantine army, departing from Gebze, landed on the shores of Yalova. Most of these Byzantine soldiers were paid Alan soldiers, numbering around 2500.

Osman Gazi was vigilant about possible assistance coming from the Byzantines. Therefore, he dispatched about 100 reconnaissance and scouting groups to the region to keep it under control. These scout groups immediately informed Osman Bey upon sighting the disembarking Byzantine soldiers. With this crucial information, Osman Gazi swiftly transported approximately 5000 cavalry troops from Yalova to İznik and confronted the attacking Byzantine soldiers at Koyunhisar in a surprise move.

The Ottoman cavalry had lain in ambush, ready to make a sudden attack on the disembarked, yet not yet organized, Byzantine army. Although the Byzantine army was composed mostly of regular soldiers, it also included local militia forces. The Turkmen army under the command of Osman Bey was an organized force consisting mainly of skilled horsemen, constituting a professional army.

Before the assembled Byzantine forces could start their march towards İznik, the Ottoman forces emerged from behind the hills and launched an attack with intense arrow fire. The local militia forces, taken aback by the fierce attack, panicked and initially started fleeing towards İzmit. This marked the first desertions from the Battle of Koyunhisar. The paid Alan soldiers were skilled fighters, and they managed to regroup and put up resistance against the Turks. Taking advantage of the resistance by the Alan cavalry, the Byzantine infantry turned back and managed to escape. While the Alan soldiers continued to fight, their strength was insufficient, and they ultimately perished in a bloody clash. In other words, the paid Alan soldiers sacrificed themselves for the survival of the Byzantine infantry.

In terms of its characteristics, the Battle of Koyunhisar may not have been a very large and intense battle, but historically, it holds great significance as the first battle between the official army of the Byzantine Emperor and the Ottoman Beylik. The location where the Battle of Koyunhisar took place is within the borders of Bursa province, which is now part of the Yenişehir district.

As a result of the Battle of Koyunhisar, there was an increase in gaza, which refers to raids from the Ottoman Empire towards the Byzantine/Roman territory. With the capture of Kite Castle, the surroundings of Bursa were completely encircled by the Ottoman principality from three sides. After the Battle of Koyunhisar, this victory brought joy and hope to the people of Anatolia, who were weary of Mongol oppression. Following this victory, the people and warriors from Anatolia pledged allegiance to Osman Bey and began migrating towards the principality he founded. According to most historians, the Battle of Koyunhisar formalized the establishment of the Ottoman state. This is because, according to ancient Turkish history, to become a state, a great victory is required, and since Osman Gazi fought and won against the Byzantine Empire, not just the Tekfurs, the year 1299 is considered as the establishment date of the Ottoman state. The fact that coins (currency) were minted in the name of Osman Gazi for the first time and that a sermon was recited in his name also occurred after the Battle of Koyunhisar, further confirming this thesis. After the Battle of Koyunhisar, Osman Gazi's prestige and status were also elevated in the face of Byzantium. In Western sources, the region where the Battle of Koyunhisar took place is referred to as Bafeus Battle due to the term 'Bafeus' in the Byzantine language.