Centro Vasco de Arquitectura
Euskal Herriko Arkitektura Ikerkundea
http://www.chesterwalls.info/oldpubs5.html
http://en.wikipedia.org/wiki/Northgate,_Chester
http://www.matthewpemmott.co.uk/2008/11/chester-city-gates-chester.html
http://www.chestertourist.com/northgate.htm