During the classical antiquity there existed an Illyrian fortress and a Roman castrum. During the reign of Byzantine Emperor Justinian, several fortified towns were built in the area. Blagaj was mentioned in Constantine Porphyrogenitus’ work De Administrando Imperio as Bona, then part of Zahumlje (Hum).
In the late 12th century, during the rule of Stefan Nemanja (Grand Principality of Serbia), prefect Jurko raised a church dedicated to saints Cosmas and Damian. In the 14th century, during the reign of Bosnian Ban Stjepan II Kotromanić, Hum became part of the Bosnian state. In the 15th century Sandalj Hranić Kosača and his nephew Stephen Vukčić Kosača ruled the Hum and Blagaj territory until the arrival of the Ottomans in 1466. Blagaj is also known as a residential area of Bosnian rulers and particularly of royal families Hranić and Kosača.
In historical sources Blagaj was first mentioned in 1423. During the period of the Ottoman Empire, Blagaj was the seat of the Blagaj Vilayet, and was divided into several neighborhoods. The city had seven mosques, two inns, four musafirhana, a madrasah (Bosnian: medresa), two maktab, seven mills and four stone bridges on the river Buna.Bosniaks were majority until 1835, during the Austro-Hungarian period Christians constituted twice as many. An Orthodox Church was built in 1893 and a Roman Catholic church in 1908.
The earliest Blagaj settlement was located at the foot of the Blagaj fort, where the road runs down from the fort and intersects with the Nevesinje road. There was too little trade for a commercial centre to emerge and in an agricultural environment of this kind the circumstances did not give rise to an urban settlement.The urbanization of the area (in the form we know today) was defined in the second half of the 15th century, and its structure was shaped during the 16th century.
Historical sources frequently refer to mediaeval fortress Blagaj Fort (Stjepan grad) as a
