The archaeological site of Fort San Lorenzo is located in the mouth of the Chagres River, Northern sector of Panama (Central America) and is one of the most important Hispanic archaeological sites of the Isthmus (17th and 18th century) because it served to protect the Chagres River-Las Cruces Trail (with the treasures from South America) from the English pirates. Two zones have been surveyed using a low-frequency multi-coil electromagnetic and magnetic (in vertical gradient configuration) devices. Maps of Zone 1 (Northeast sector) show an alignment along the surveyed area which may be linked with a trench used as a strategic military route and a boundary between the hornwork of the main structure with the external battery. Maps of Zone 2 (Central Sector) show a portion of a buried wall, possibly linked to an important structure of the Fort.