Colonia del Sacramento (kōlō`nyä thĕl säk'rämān`tō), city (1996 pop. 21,744), capital of Colonia dept., S Uruguay, on the Río de la Plata. It is a resort city, a port, and the trade center for a rich agricultural region. The city, founded by the Portuguese in 1680, was bitterly contested before being ultimately secured by the Spanish. Colonia has many fine examples of colonial architecture.