Numbers 10:1-5

The LORD spoke further to Moses, saying, “Make two trumpets of silver; you shall make them of hammered work. You shall use them to summon the congregation and to have the camps move out. When both are blown, all the congregation [that is, all adult males] shall gather before you at the doorway of the Tent of Meeting (tabernacle). However, if a single trumpet is blown, then the leaders, heads of the tribes of Israel, shall gather themselves to you. When you blow an alarm, the camps on the east side [of the tabernacle] shall set out.