In this work the results of a geomagnetic study of the subsoil are presented in a place that conforms one of the most important historic legacy of Panama: The Joint one Monumental of Panama Viejo. With the objective of knowing the nature of the soil and the answer of the activity of the man in the past upon said region, an cartographical analysis of the vertical magnetic gradient was carried out. Studying the rank of the magnitude and the sign of polarity of the own magnetic anomalies of place, was possible to detect in a zone, two periods of occupation: one of hispanical type and the other more recent one of last century (zone 1), and another zone located a little more toward the east of the first one, with a notable extension of volcanic rocks (zone 2).