Fort Kastella, Portuguese fort in Ternate, Indonesia.

Fort Kastella is a ruined Portuguese fortress on Ternate's southwest coast, near the Sultan's court but 7 km from the reef-free harbor at Talangame. Its remains are scattered over a wide area among local houses and cut by the island's main road. Sections of old walls and bastions from the Spanish period still stand, and a monument marks the 1575 Ternatean victory over the Portuguese.

In April 1521 King Manuel I of Portugal sent a fleet under Jorge de Brito to intercept Magellan's ships and build a fortress on Ternate. The first stone of São João Baptista was laid in 1522 and the fort was completed on 15 February 1523. After Sultan Hairun was killed in 1570, Sultan Baab's forces besieged the Portuguese for five years; in 1575 they surrendered the fort and withdrew to Ambon.

Locals call the site Kastella, after the Spanish region of Castile, a name that outlasted the Portuguese, Ternatean and Spanish occupations. Sultan Baab turned the captured fort into his royal palace and renamed it Gammalamma. A monument at the ruins commemorates the 1575 Ternatean victory over the Portuguese.

The ruins lie on the southwest coast of Ternate, split by the island's main road and mixed among local houses, so the site is seen in separate pieces rather than as one enclosure. Sections of the old walls and Spanish-period bastions remain visible, and a monument marks the 1575 Ternatean victory over the Portuguese.

The site's monument commemorates the 1575 victory of Sultan Baab's forces over the Portuguese, who had held the fort since 1522. Sections of walls and bastions from the Spanish period, when Kastella served as the Spanish capital of the Moluccas from 1606 to 1663, remain visible among the houses.