Through the Middle Ages Copenhagen was protected by outer defences - initially a timber palisade but later substantial walls and towers. By the early 16th century there were eleven towers around the city but only one, the round tower at the south-west corner of the city at Jarmers Plads, can be seen now and only the lower part of the tower survives. It was covered over when an embankment was constructed to improve the defences in the 17th century but was excavated in the 1880s when the embankments on this side of the city were removed.
This tower dates from the early 16th century with a stone core to the thick walls but faced inside and out with brick. The outer face is decorated with large diamond shapes in the brickwork formed by carefully arranging darker bricks in the bonding. In England these darker bricks are called fired or burnt headers and were formed where bricks were stacked in the kiln to be fired and only the outer bricks of the stack, exposed to the flames and higher temperatures, changed to this dark, grey, colour.
The round tower had a doorway into the lower part from the town side but presumably upper levels were accessed from a walkway on the top of the wall.