(Scroll down for the answer)
(because there were twelve tribes of Israel)
Lord spoke to Moses saying, "Send out for yourself men so that they may
spy out the land of Canaan, which I am going to give to the sons of Israel;
you shall send a man from each of their fathers' tribes, every one a leader
among them." So Moses sent them from the wilderness of Paran at the command
of the Lord, all of them men who were heads of the sons of Israel.