In medieval fortification, a tower built beside or over a gate, as of a city, etc., for the purpose of defending the passage.(noun)
The Century Dictionary (Public Domain)
Use "gate-tower" in a sentence
"Kharl felt as though he were more staggering than anything else as he followed Hagen down the gate-tower steps, back across the courtyard, then around the north side of the Great House."
"So I established myself in its southern gate-tower, and set my six Haurani boys (for whom manual labour was not disgraceful) to cover with brushwood, palm-branches, and clay the ancient split stone rafters, which stood open to the sky."
"And at the very top of the topmost bluff he could just see a streak of dark wall broken by a gate-tower."