Archaeological investigation has determined that the various types of mounds were arranged in a planned construction that reflected the cosmology of the Mississippians. The smaller ridge-top and conical mounds were used for ritual burials, some for elites and some for apparent sacrifices. The larger platform mounds were used for temples and homes of the elite. Archaeologists have found remains of a long, defensive wooden stockade that enclosed the central precinct and was rebuilt several times. They also discovered two major solar calendars, now known as Woodhenge, as the works were constructed of cedar, which was considered a sacred wood. The area surrounding the mounds had numerous borrow pits from which soil was taken to build the mounds and to fill and level the Grand Plaza and other plazas.