He sounded the call to action, rallying everyone to move.
Tips
history
Earliest attested in the Yuan-era zaju play 《午时牌》. In ancient Chinese armies, drums (鼓) signaled advance and the bronze gong (金 = 锣) signaled retreat — so the four characters together capture the whole battlefield communication system.
memory
擂 (beat) 鼓 (drum) 鸣 (sound) 金 (gong/metal) — beat-drum, sound-gong. Two parallel verb-object pairs, easy to remember as an action diptych.