A large earthwork system north of the Classic Maya center of Tikal, Guatemala was discovered in 1966 by University of Pennsylvania archaeologists. The system consisted of a ditch and an inner embankment and was presumably used as a fortification. At certain locations, the ditch was bridged by causeways. Our goal was to analyze the soils that were used and manipulated in connection with the earthwork. Our study included various cross sections of the earthwork and one of the bridged causeways that intersected the earthwork. The earthwork profiles contained a variety of buried A horizons. These were collected and described. Soils from A horizons beneath the embankment were compared with modern A horizons. Soil phosphorus levels were analyzed to learn about the nature of the causeway. The results provide information on soil erosion, ancient agriculture, and land use.