Deuteronomy 27:13

Mount Ebal. This mountain lies north of Shechem, opposite Gerizim, with a narrow valley in between. The two mountains thus formed a large natural amphitheater, of sufficient size to accommodate the vast throng. The speakers were to stand in the center, in the valley; the tribes were to assemble on the slopes of the two mountains. Six of the tribes descended from Leah and Rachel were to respond to the blessings. The tribes by whom response was to be made to the curses for disobedience, were the descendants of Zilpah and Bilhah, together with those of Leah’s youngest son, Zebulun, and of Reuben, who forfeited his birthright because of his sin against his father (Gen. 35:22; 49:4).