The Israelites were commanded to organize a mass gathering upon their entering the Land of Israel, to bless those who will follow the proper path and to curse those who will deviate from it. The curses appear explicitly in the Torah, and the Sages explain that the blessings and curses were formulated in ways parallel to each other. The Sages describe this event.

How did the stating of blessings and curses take place? When the Israelites crossed the Jordan and arrived at Mount Gerizim and Mount Eival in Samaria, alongside Shekhem…. Six tribes ascended to the top of Mount Gerizim and six tribes ascended to the top of Mount Eival, and the priests and the Levites and the ark were standing at the bottom, in the middle. The priests were around the ark and the Levites were around the priests, and all the rest of the Israelites were standing on the mountains on this side and on that side….

The priests and the Levites then turned to face Mount Gerizim and began with a blessing: Blessed is the man who will not craft an idol or a cast figure, and these people and those people, those standing on both mountains, answered: Amen. Then they turned to face Mount Eival and opened with the curse: “Cursed is the man who will craft an idol or a cast figure” (Deuteronomy 27:15), and these people and those people answered: Amen. The priests and the Levites continued until they completed reciting all the blessings and curses. (Mishna Sota 7:5)