Ancient Greek religious practice, essentially conservative in nature, was based on time-honored observances, many rooted in the Bronze Age (3000–1050 B.C.), or even earlier. Although the Iliad and the Odyssey of Homer, believed to have been composed around the eighth century B.C., were powerful influences on Greek thought, the ancient Greeks had no single guiding work of scripture like the Jewish Torah, the Christian Bible, or the Muslim Qu’ran. Nor did they have a strict priestly caste. The relationship between human beings and deities was based on the concept of exchange: gods and goddesses were expected to give gifts. Votive offerings, which have been excavated from sanctuaries by the thousands, were a physical expression of thanks on the part of individual worshippers.​