It is only in the last 200 years that museums or art galleries have been built for their specific purpose. Before the 19th century, adaptation of pre-existing spaces was the rule. Conversion/adaptation of historic buildings to serve as museums has recently become economically desirable. Cannon-Brookes provides the historic background for the trend toward adaptive use, presenting the Palais du Louvre as an example. He then sets down general principles for determining the degree of intervention that will be necessary and discusses the major disadvantages and problems of converted spaces (conformation to modern safety regulations). The building housing the Czech National Gallery (Prague), a former convent, is presented as a modern example of adaptive use.