Evidence of human presence since the Neolithic period has been found there. Oretans was the name of the Iberian tribe which settled in the vicinity in the north of the Guadalquivir River beginning in the sixth century BC. Of tradition, a local princess named Himilce married Hannibal and gained the alliliance of the city with the Carthaginian Empire.
In 213 BC, Castulo was the site of Hasdrubal Barca's crushing victory over the Roman army with a force of roughly 40,000 Carthaginian troops plus local Iberian mercenaries. Thereafter the Romans made a pact with the residents of city — who then betrayed the Carthaginians — and the city became an foederati (ally) of Rome.
|O: diademed head||R: bull, crescent above, KAŚTILO retrograde below|
|bronze semis struck before 214 - 212 BC in Castulo
ref.: CNH p. 331, 2-3; SNG BM Spain 1223-6 
Castulo lost importance even more when Andalusia fell under Islamic rule in the Middle Ages, and at the same time the nearby village of Linares grew because of its strong castle —first built as an Arab fortress, then rebuilt by the Christians after the Reconquista— overlooking the city. In 1227 the walls of Castulo were destroyed, and the town was depopulated shortly afterwards.
A Bishopric of Castulo was established around 350 AD on territory split from the Andalusian diocese of Tucci (now also a titular see). Information about Christian bishops of Castulo appears in the first half of the fourth century AD through participation by its bishops in the Council of Elvira and that of Sardica. It may have been reabsorbed by Tucci.
The diocese reappears two centuries later, when in 589 a bishop of Castulo, which by then was under Visigoth rule and a suffragan of Toledo, took part in the third Council of Toledo. Other bishops of Castulo were at later Visigoth councils down to the tenth Council of Toledo in 656. Thereafter, Castulo is replaced as bishopric by the Diocese of Baeza. Enrique Flórez,
It was nominally restored in 1969 and since has had the following incumbents:
- Titular Archbishop Angel Maria Ocampo Berrio, Jesuits (S.J.) (1970.02.20 – 1973.03.10)
- Titular Bishop Enrico Bartolucci Panaroni, Comboni Missionaries (M.C.C.J.) (1973.06.14 – 1995.02.10)
- Titular Bishop Riccardo Ruotolo (1995.12.06 – 2012.08.01)
- Titular Bishop Adelio Dell’Oro (2012.12.07 – 2015.01.31)
- Spann, P., DARMC, R. Talbert, S. Gillies, J. Åhlfeldt, R. Warner, J. Becker, T. Elliott. "Places: 265855 (Castulo)". Pleiades. Retrieved 13 December 2014.
- Rome and Carthage
- España Sagrada, volume VII, Madrid 1751, pages 134–160
- A. Lambert, v. Beacia, in Dictionnaire d'Histoire et de Géographie ecclésiastiques, vol. VII, 1934, coll. 79-80
- Annuario Pontificio 2013 (Libreria Editrice Vaticana 2013 ISBN 978-88-209-9070-1), page 863
- A Brief History of Spain - Carthage and Rome 
- "CÁSTULO (Cazlona) Jaén, Spain." In The Princeton Encyclopedia of Classical Sites edited by R. Stillwell et al. 1976.
- GigaCatholic, with titular incumbent biography links