The Classic Maya built many of their temples and palaces in a stepped pyramid shape, decorating them with elaborate reliefs and inscriptions. These structures have earned the Maya their reputation as the great artists of Mesoamerica. Guided by their religious ritual, the Maya also made significant advances in mathematics and astronomy, including the use of the zero and the development of a complex calendar system based on 365 days. Though early researchers concluded that the Maya were a peaceful society of priests and scribes, later evidence–including a thorough examination of the artwork and inscriptions on their temple walls–showed the less peaceful side of Maya culture, including the war between rival Mayan city-states and the importance of torture and human sacrifice to their religious ritual.