Structure B1-1 is the principal structure in the Tazumal group and dominates the complex. The pyramid underwent various phases of construction through the Classic and Early Postclassic periods. Structure B1-1 was built upon a basal platform, called the Great Platform by Boggs, that measures (east-west by north-south). The pyramid was surveyed in 2003–2004. A long platform runs north-south along the western facade of the pyramid and a platform of similar length runs east-west along the north side of the structure. These two side platforms were originally built as separate structures but were later incorporated into the Great Platform; it is presumed by investigators that the temple was radially symmetrical and that further platforms existed on the east and south sides. The remains of a platform measuring were found in roughly the correct position for such a platform on the east side. A test pit sunk into the presumed area of the southern platform uncovered an offering containing a cylindrical ceramic vessel with a polychrome bowl placed upon it like a lid. Within the vessel were two larger pieces of jade and 50 smaller jade fragments, a fragment of seashell and a fragment of snail shell, various pieces of animal bone, mica and traces of red pigment. The offering was covered with a slab of stone. The cylindrical vessel was decorated with two panels, each containing a personage wearing a headdress and performing autosacrifice.