Info : http://fr.wikipedia.org/wiki/Tour_du_Leughenaer

The Tour Leughenaer is an octagonal tower 30 meters high in Dunkirk. Built around 1450, this tower is the oldest monument in the city. It was built by Jacques Desfontaines surrounded the 18th century a platform port monitoring and enhanced in 1814 to install a lighthouse lantern. It has retained much of its 19th century1 technical devices.
The Tour Historic Monument in 19951.

Legend wreckers
This is after it was built it was rigged the nickname "Tour Liar". It was so named after the grounding, on the sandbanks of the harbor, many boats yet guided by signals from its summit. Over the years, the legend of "wreckers" took shape: the Dunkirk would have sent the wrong signals to intentionally fail boats and loot. In fact, if some ship never reached the port, it was mostly because the channel is too tortuous access