Grotefend extended this work by realizing, based on the known inscriptions of much later rulers (the Pahlavi inscriptions of the Sassanid kings), that a king's name is often followed by “great king, king of kings” and the name of the king's father. This understanding of the structure of monumental inscriptions in Old Persian was based on the work of Anquetil-Duperron, who had studied Old Persian through the Zoroastrian Avestas in India, and Antoine Isaac Silvestre de Sacy, who had decrypted the monumental Pahlavi inscriptions of the Sassanid kings.