The Fortaleza de São João da Barra do Rio de Janeiro (Portuguese for: Fortress of Saint John of the Harbor of Rio de Janeiro), popularly known as the Fortaleza de São João or Forte (de) São João (Fort (of) Saint John), is a 16th-century star fort in the present-day Urca neighborhood of Rio de Janeiro, erected by Estácio de Sá to protect Guanabara Bay from French invasion.