Fort Kastela is a ruined Portuguese fortress located at the southwest coast of Ternate. It is famous for being the first colonial fortification constructed in the Spice Islands (Maluku) of Indonesia. Built by the Portuguese in 1522, it is also referred to in different languages as São João Baptista de Ternate or Fortaleza de Ternate (Portuguese), Ciudad del Rosario (Spanish) or Gammalamma. Today it is locally known as Kastella/Kastela.

Ternate, also known as the City of Ternate, is a city in the Indonesian province of North Maluku and an island in the Maluku Islands. It was the de facto provincial capital of North Maluku before Sofifi on the nearby coast of Halmahera became the capital in 2010. It is off the west coast of Halmahera, and is composed of eight islands: Ternate, the biggest and main island of the city, and Moti, Hiri, Tifure, Mayau, Makka, Mano, and Gurida. In total, the city has a land area of 162.20 square kilometres and had a total population of 185,705 according to the 2010 census, and 205,001 according to the 2020 census, with a density of 1,264 people per square kilometre; the official estimate as at mid 2023 was 204,920. It is the biggest and most densely populated city in the province, as well as the economic, cultural, and education center of North Maluku, and acts as a hub to neighbouring regions. It was the capital of the Sultanate of Ternate in the 15th and 16th centuries, and fought against the Sultanate of Tidore over control of the spice trade in the Moluccas before becoming a main interest to competing European powers.