The National Library of Greece is hosted in a magnificent neo-classic complex of URM buildings built at the beggining of the 20th century, which has been damaged by the 07.09.99 Athens earthquake. In order to achieve a light and reversible intervention the design consisted of extensive in situ and laboratory tests concerning the mechanical, chemical and mineralogical characteristics of masonry, special considerations for the composition of the enamas to be used in order to prevent any impact on the frescos, and sophisticated analytical models and procedures including a pushover analysis and evaluation using the ADRS methodology.