The Spanish Empire constructed the Portobelo-San Lorenzo fortifications during the 17th and 18th centuries on the Caribbean coastline of Colón Province in Panama. These ruins were included by UNESCO on the World Heritage List due to their cultural importance, as they are magnificent examples of 17th and 18th century military architecture. The fortifications are located approximately 80 kilometres (50 miles) apart, with Portobelo providing cover on the Caribbean side of the Panama harbour, and San Lorenzo protecting the Chagres River at its mouth. The port was built as an alternate route to Nombre de Dios for transatlantic trade, in order to avoid the land route affected by the rainy season. Additionally, a combination of a waterway and terrestrial route was built from the Chagres River to Cruces as an alternative approach to Portobelo via Camino Real and Panama City.