Coriantumr’s trumpet is the trumpet Coriantumr sounded from the hill Comnor to summon Shiz’s armies to battle. Coriantumr gathered his armies upon the hill Comnor and “did sound a trumpet unto the armies of Shiz to invite them forth to battle” (Ether 14:28).
Coriantumr pitched his tents in the valley of Shurr, which was near the hill Comnor, while the opposing tents were in the valley of Corihor (Ether 14:28).