Henry Petroski, "To Forgive Design: Understanding Failure" Cambridge, Mass: Belknap Press of Harvard University Press, 2012, ISBN 9780674065840.
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By June 11, 1937, the Basque forces had fallen back to the city of Bilbao, which was defended by a series of rushed fortifications called the "Bilbao's Iron Ring." The Iron Ring was poorly designed for defense.
However, it was quite an antiquated defence concept akin to First World War fortifications, so it was vulnerable to modern warfare weapons of its time such as aircraft and artillery, and only 30,000 troops were defending it (it was conceived to be defended by 70,000) — therefore the Iron Ring was rather easily overcome by the Nationalist faction forces in the battle of Bilbao.
He ended his boycott of the Diet and Reichstrat in 1879, and was one of the leaders of the federalist majority supporting Count Taaffe's conservative coalition of Iron Ring.
He was largely responsible for the creation of the Ritual of the Calling of an Engineer administered to many Canadian engineering students, where they receive the Iron Ring.
The earliest written law from what is now Sweden seems to be the Forsaringen, an iron ring from the door for the church of Forsa in Hälsingland, which carries a runic inscription, long thought to be from the high Middle Ages but more recently dated to the ninth or tenth century.