Jamieson, Fausset and Brown on Zephaniah 1:16

16. the trumpet--namely, of the besieging enemy (Am 2:2).

alarm--the war shout [Maurer].

towers--literally, "angles"; for city walls used not to be built in a direct line, but with sinuous curves and angles, so that besiegers advancing might be assailed not only in front, but on both sides, caught as it were in a cul-de-sac; towers were built especially at the angles. So Tacitus describes the walls of Jerusalem [Histories, 5.11.7].