Columbus coasted along the entire eastern shore of Central America, from Cape Honduras to Nombre de Dios, or Chagres, in 1502, and was probably the first discoverer of the Port of San Juan. In 1529, Captain Diego Machuca, residing in the city of Granada, on Lake Nicaragua, undertook the exploration of that lake, discovered its outlet, passed down the San Juan to the port at its mouth, and sailed thence to Nombre de Dios. The principal rapids in the stream still bears his name. We are informed by the historian Gonzalo Fernandez de Oviedo y Valdez, who was in Nicaragua in 1529, and was personally acquainted with Machuca, that the latter projected a colony at the mouth of the river, but was interrupted in his design by Robles, commandant at Nombre de Dios, who contemplated the same enterprise. At how early a date the Spanish made establishments at San Juan, is not known; but it is a historical fact, that early in the seventeenth century a fort existed at San Carlos, which was captured by the English in 1665, but recovered by De Mencos and De Caldas, officers of Spain in the then Kingdom of Guatemala. (_Juarros’ History of the Kingdom of Guatemala_, _Baily’s Trans._, p. 67.) In consequence of this event, a royal decree was issued, commanding that the entrance of the river should be fortified; which order was carried into effect by Don Fernando de Escobeda, who examined the port and river, and built a fort in obedience to his instructions. It is also a historical fact, that at the period of the _rebuilding_ of the Fort of San Juan, on the river above, about 1727, a garrison was maintained here. At that time not less than twelve military stations existed on the river; the first was at San Carlos, at the head of the stream; the second at the mouth of the Rio Savalos; the third, a short distance from the mouth of the Rio Poco Sol; the fourth, the Castle of San Juan; the fifth, the Island of Bartola; sixth, a high bank below the Rapids de los Valos, called “_Diamante_;” seventh, at the Rapids of Machuca; eighth, on an island at the mouth of the River San Carlos; ninth, at the mouth of the Rio San Francisco; tenth, at the mouth of the Serapiqui; eleventh, at the point called “Conception,” opposite an island of the same name; and twelfth, at the Port of San Juan itself, with an intermediate temporary station called “Rosario.”