A day of the trumpet and alarm against the fenced cities, and against the high towers.
A day of the trumpet - namely, of the besieging enemy (Amos 2:2, "Moab shall die with tumult, with shouting, and with the sound of the trumpet").
And alarm - the war shout (Maurer).
And against the high towers - literally, angles; because city walls did not used to be built in a direct line, but with sinuous curves and angles, so that besiegers advancing might he 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 ('History,' 5: 11, 5).