São Marcelo Fort (Portuguese: Forte São Marcelo), also known as Forte de Nossa Senhora do Pópulo e São Marcelo or Forte do Mar, is located in Salvador in Bahia, Brazil. It is located in small bit of land off the coast in the Baía de Todos os Santos. Standing on a small bank of reefs about 300 metres (980 ft) from the coast, it is one of two forts separated by water from land in Brazil, the other being the in Rio de Janeiro. It is the only cylindrical fort in Brazil. Its design follows those of Castel Sant'Angelo in Italy and São Lourenço do Bugio Fort in Portugal. It is popularly known as the "Forte do Mar" (Fort of the Sea). It was built to protect the important port city Salvador from threats; the city had the largest number of forts during the colonial period of Brazil.