At the top of the cobbled alley leading up from the "La Piraille" neighborhood, one could access the upper town via a postern (posty, sentry post), which was demolished in 1822. The last resident of this sentry post was F. Harlequin: he first gave his name to the posty and later to the steep alley. For several centuries, this alley was nothing more than a muddy ditch beneath the city walls, collecting all the dirty water from the town hall, which was located within the Notger city walls (10th century). Thuin was a fortified town and successively built three ramparts around the town halls of the four neighborhoods: "le Marchet," "la Crapaure," "la Grand'Rue," and "le Crepion." After the wars against Burgundy, Thuin was forced to demolish its ramparts and towers. The brick tower that currently stands behind the houses encloses the foundations of a massive corner tower made of rubble stone. This tower is still part of the first wall that Notger, the first Prince-Bishop of Liège, had built in the tenth century.