In the 11th and 12th centuries thinkers argued that human society consisted of three orders: those who pray, those who fight, and those who labour. The structure of the first order, the clergy, was in place by 1200 and remained singly intact until the religious reformations of the 16th century. The second order, those who fight, was the rank of the politically powerful, ambitious, and dangerous. Kings took pains to ensure that it did not resist their authority. The general category of those who labour (specifically, those who were not knightly warriors or nobles) diversified rapidly after the 11th century into the lively and energetic worlds of peasants, skilled artisans, merchants, financiers, lay professionals, and entrepreneurs, which together drove the European economy to its greatest achievements.