The Watch Tower is 35 metres high. This tower is probably one of the oldest monuments in the city. In the thirteenth century It was the centre of a medieval castle. Its date of construction is uncertain. Some say that it could be a tower that Charlemagne constructed about 810 in order to protect the coastline against Norman invasions. The first official date is 1302.
In 1580 The tower threatened to collapse following an earthquake that split the tower in two. As its name indicates, the Watch Tower  sheltered a service of lookouts, until 1905. In 1818, the tower was arranged as a beacon of rotating lights. This was replaced in 1848 by the present lighthouse. It was classified an historic monument in 1931.

Construction of the Calais Lighthouse started in 1845 and functioned for the first time in 1848. to substitute the old Watch Tower. It first operated with oil then from 1883 with electricity . The lantern gives out four bursts followed by a gap of seven seconds. Its range is about 32 kilometres