According to the Bible, Abraham was the first to establish a covenant with God through his self-circumcision at the ripe old age of 99. This act is symbolically repeated with each generation of Jewish males. Abraham's grandson Jacob fathered twelve sons from whom descended twelve tribes, the nation of Israel. Abraham, his son Isaac, and his grandson Jacob are believed to be buried with their wives, Sarah, Rebecca, and Leah, in the Cave of the Makhpelakh in Hebron . Because Ishmael, Abraham's other son, is believed to be the ancestor of Islam, this resting place is holy to both faiths. The Bible says that the founding period of the Israelite nation was the genera- tion spent wandering in the Sinai desert en route from Egypt to the Holy Land, under the leadership of Moses. It was this generation that received the Torah, the central text of Judaism, at Mt. Sinai . Historians theorize that the dis- parate tribes later known as the Israelites had gradually united under a common god by the third millennium ВСЕ. This god, Yahweh, is thought to have been a young, warlike version of the older Canaanite deity, El . Some scholars believe Yahweh was introduced to the highland Canaanites by Semitic tribes escaping from Egypt, and that he was worshiped as an alternative to the lowland storm-god, Ba'al. When the Israelites formed a king- om, worship of God was centralized in the capital, Jerusalem. The religion came focused around the Temple, or belt hamikdash, where sacrifices were rought under the supervision of the priests, or kohanim. However, Judaism ecame decentralized after the destruction of the first Temple. Prayer replaced sacrifices as a significant daily ritual, taking place three times a day on weekdays and four times a day on the sabbath and on holidays. Historians estimate the present form of the Torah to be 2500 years old, although it has been continuously interpreted and re-interpreted over the centuries in an effort to maintain its vitality and apphcability. The Written Torah , which consists of the first five books of the Bible, formed the template for the Oral Torah, a series of interpretations and teachings eventually codified in final form around 200 CE as the Mishnah. The Gemara then formed an additional layer of interpretation. The Mishnah, along with the Gemara, form the basis of the Babylonian and Jerusalem Talmud, final- ized during the 5th century CE. The Talmud, organized as a transcribed series of discussions aimed at interpretation of the Mishnah, was the springboard for a new series of interpretations that continue to build upon each other. "Torah," which has come to refer to all Jewish thought and teachings, has been at the core of Jewish life through most of history. In Judaism, faith in God is central, but the energy of Jewish life is concentrated on observing the commandments. The Torah contains 613 mitzvot , including directives for ritual observances and instructions concerning moral behavior.