According to the Cañas-Jerez Treaty of 1858, as reaffirmed and interpreted by the arbitration of U.S. president Grover Cleveland in 1888 and by the judgment of the Central American Court of Justice in 1916 , the border between Nicaragua and Costa Rica runs along the right bank of the San Juan River, from its mouth in the Caribbean port of San Juan del Norte (formerly known as Greytown), to a point located downstream from an old fortification known as Castillo Viejo ("Old Castle"), originally built to guard the access to Lake Nicaragua.Grover Cleveland, "Award of the President of the United States in Regard to the Validity of the Treaty of Limits Between Costa Rican and Nicaragua of 15 July 1858, Decision of 22 March 1888." First published in John Basset Moore, History and Digest of the International Arbitrations to Which the United States has been a Party, vol. II (Washington, D.C.: Government Printing Office, 1898), p. 1946. Reproduced in the United Nations Reports of International Arbitral Awards, vol. XXVIII, pp. 189-236 (2006)
