The origins of the Diocese of Cartagena are uncertain, but it is known that they are somehow related to the arrival of the Apostle James in Spain at the port on the southern coast of Murcia. Neither is Santiago the only Saint connected to Cartagena, as four siblings from the city are also still much in evidence there (San Isidoro, San Fulgencio, San Leandro and Santa Florentina).
Over the centuries the Diocese has left an important mark on the history and heritage of the Region, including the old Cathedral of Cartagena which was built following the reinstatement of its diocesan status in 1250. This was granted due to the efforts of Alfonso X, who requested it from Pope Innocent IV.
Another of the most important points in the history of this body came two decades later, when Bishop Diego de Madaz requested the transfer of the episcopal seat to the city of Murcia, and after various refusals this too was granted in 1291 by Nicholas IV. However, despite the administrative and religious institution being based in Murcia, the Diocese has retained the name of Cartagena until the present day.