Fort Cobo (Tjsobbe) is located on the spur of a steep hill at Soasiu on Tidore in North Maluku. The Spaniards and the people of Tidore built the fort in 1637. Due to its location the fort controlled both the Palace of the Sultan of Tidore in Saosiu and the shipping through the Strait between Tidore and Halmaheira. The Spaniards briefly left the fort, but they returned in 1640.
In 1664 the Spaniards abandoned all their forts in the Moluccas and withdrew to the Philippines. The inhabitants of Ternate occupied the three empty Spanish forts (Cobo, Tahula and Rum) on the island and claimed them as their property. The Dutch East India Company demanded the demolition of the forts. After negotiations both parties reached an agreement in 1666. The forts Tahula and Cobo were transferred to the sultan and fort Rum dismantled. The sultan used fort Cobo as barracks for his European bodyguard.
After 1700 the fort fell into decline. In 1928, the only visible remains were the powder house, the gate, a part of the sea-bastion and the walls of some buildings. In 2007, a large part of the hill and the fort excavated for the construction of the coast road.