The Ponttor is one of the two remaining gates of the original city wall of Aachen. It was built in the 14th century and manned by soldiers and militia throughout the Free Imperial City of Aachen era. Today, the Ponttor is used by German Youth and Scout groups.
The Ponttor was constructed as a right-angled three-stock tower castle. In the main entrance, there is a Portcullis as well as a machicolation, through which things could be dropped on invading forces. A bridge passage with crenelations spanned a moat and was strengthened in the foregate with two reinforced towers (barbicans). The building material was Devonian sandstone, Pennsylvanian carbonite sandstone and quartzite, with the framing material made of light bluestone.
References:The Citadelle of Quebec is an active military installation and official residence of both the Canadian monarch and the Governor General of Canada. It is located atop Cap Diamant, adjoining the Plains of Abraham in Quebec City. The citadel is the oldest military building in Canada, and forms part of the fortifications of Quebec City, which is one of only two cities in North America still surrounded by fortifications, the other being Campeche, Mexico.
The first fortifications in Quebec were built by the Governor General of New France Louis de Buade, and completed just in time for the Battle of Quebec in 1690.
After the British conquest in the second half of the 18th century, the problem of Quebec City's defences grew more acute.