Brugge : The gables

there are hundreds of stepped gable walls which are the familiar skyline in Bruges.. The style was popular from the 14th through the 18th century; and enjoyed resurgence in 1880, when restoration work was carried out in the city. It is thought that this style originated in Amsterdam or in Lubeck, Germany, where, like in Brugge, many buildings overlook canals and quaysides.  (source : virtual tourist.com/medieval architecture)

A gable wall is a section of a building's outside wall that is shaped like a triangle and that is formed by two sections of the roof sloping down (Webster dictionary)