The diagram shows end elevations and a plan of a standard watchtower.

Each tower stands guard on a gate which allows passage from one province into another through the wall that carries a leftway.

From the summit of a watchtower, six ribs curve up holding aloft a platform at the centre of which is located a heliograph mechanism. Two of the ribs are piped so that naphtha can be burned in flares to transmit signals during the night when the heliograph cannot work.

The ribs emerge from a keel beam at the ends of which are two of the four deadman chairs. The other two are hung from the upper ends of the middle ribs. Lookouts sitting in these chairs maintain a constant scrutiny of the Guarded Land as well as on the road below.

The keel beam is embedded in the superstructure of the tower which consists of a number of floors: those above the level of the leftway are connected by ladders that can be raised by means of counterweights. Those below the level of the leftway are connected by ramps.

Note the drawbridge which allows the leftway to span the gateway below.