The Rumichaca Bridge (Quechuarumi stone, chaka bridge, "stone bridge") is the principal passage between Colombia and Ecuador. The stone bridge was built by the Incas. To one side of the artificial bridge, there is a natural stone bridge that rises over the Carchi River. On this natural bridge are the Colombian and Ecuadorian customs houses. These were built in the 19th century and have been remodeled to be binational centers of culture and tourism where the integration of the two countries is promoted. Commerce between Colombia and Ecuador has made this bridge the principal artery for the transport of goods between the countries.