Belfast, Irish Béal Feirste, city, district, and capital of Northern Ireland, on the River Lagan, at its entrance to Belfast Lough (inlet of the sea). It became a city by royal charter in 1888. After the passing of the Government of Ireland Act, 1920, it became the seat of the government of Northern Ireland. The district of Belfast has an area of 44 square miles (115 square km). The site of Belfast was occupied during both the Stone and Bronze ages, and the remains of Iron Age forts are discernible on the slopes near the city centre. A castle, probably