Boron carbide (B4C) was synthesized from the elements at temperatures ranging from 1300 degrees to 2100 degrees C using the spark plasma synthesis method. Significant densification commenced at about 1500 degrees C and was accompanied by a corresponding decrease in the defect structure of this carbide. Changes in the X-ray diffraction patterns were in agreement with predictions of simulation studies based on the presence of twins. Transmission electron microscopy observations were consistent with the experimental observations and the modeling predictions.