In 1605 a punitive expedition under Gen Juan Manuel de la Vega was sent to Tandag, but at the sight of the fleet the bellicose inhabitants, called Caragas, withdrew to the mountains. However, the inhabitants continued resisting Spanish attempts to establish a colony on Mindanao’s Pacific or eastern coast and were raiding the nearby Visayan islands for slaves. To put an end to the Caraga slave raider, in 1609, Gov Gen Juan de Silva sent a fleet with more than 400 Spanish and native soldiers. He also had a fortification built. His strategy was to contain the natives before they could organize as slaving parties.
Thus, Fort San José in Tandag was built to contain the local tribes rather than to repel raiders who came through sea. The fort was soon put to the test when 3000 Caragas attacked the fortification—unsuccessfully.
Later, however, as the inhabitants of Tandag had converted to Christianity, the fort functioned like other forts in the archipelago as coastal defense. And this was their principal purpose during the height of the Moro raids.
In 1622, the bishop of Cebu, Pedro de Arce, entrusted the care of Tandag to the Recollects. From Tandag the friars, initially eight of them, set out to convert the surrounding villages, from Gigaquit to Siargao Island. In 1754, Maguindanaos attacked Tandag. Despite great odds the defenders held on as long as they could. But the fort was breached and damaged during battle. But as result of the raid, the town was eventually abandoned. It is not clear what happens to the fort at this point. Was it abandoned? Or did a garrison remain to keep and man the fort?
In 1761 and 1767, the fort was attacked again suggesting that the fort was apparently rebuilt after the 1754 battle. During the 1767 attack, Fray Valerio de San Agustin who had left Tandag to establish the town of Cantilan returned with force of 200 native militia and seven armed sailboats. His timely intervention saved Tandag but at the cost of heavy casualties.
The fort was in a bad state in 1796, when it was recommended that it was better to abandon the fort and transfer the troops, half to Baganga (now Davao Oriental) and half to Caraga. A report of 1797 stated that the fort was in ruins because of an earthquake, the storeroom was completely useless and the prison wall was nothing more than wooden stakes and that another earthquake would completely demolish the fort. However, Schreurs remarks “The fort was obviously not demolished” despite the fort’s destruction in 1613 and the 1754 siege by the Maguindanaos and the damaged caused by the 1796 earthquake, Schreurs argues that the ruined fort stood until 19th century, because a document in the series “Erreccion de Pueblos, Carga desde 1820 hasta 1823” (RMAO), mentions that in 1821 “one day 18 Moro pancos sailed passed the baluarte de San José de Tandag.” Then, the fort had garrison had a contingent of one corporal and three soldiers.
The fort was triangular with two unequal bastions at the corners and third demi-bastion as noted in the 1738 Valdes Tamon report.
Only the foundations of the fort remain today but is barely significant.