Units are recruited centrally and are deployed into special structures called "citadels" which range from castles to wooden watchtowers.

Further investigations conducted in 1920 resulted in the belief that the five stones found by Cortis were foundations of a wooden watchtower.

It consisted of a cleared zone of observation, a palisade where practicable, wooden watchtowers and forts at the road crossings.

A log wall, nearly twenty feet tall, surrounded the town, with wooden watchtowers scattered along its length.

One of the legs of the great wooden watchtower was blasted away as the shot smashed a hole in the palisade in front of it.

Primary wooden watchtower with piling and moat, stone watchtower built in the 12th century.

Guards armed with spears looked at them from wooden watchtowers on either side of the entrance.

The village's namesake might have been a wooden Roman watchtower, also called "Katz".

A single gate faced them, some twelve feet tall and ten wide, with a wooden watchtower on each side.

Deeply into the camp, they came to a region of high wire gates and fences, surrounded by wooden watchtowers.