The operative period of the Masonic fraternity flourished from the 11th to the 15th centuries. The 16th century saw the rise of the Reformation in Europe, and the Gothic style of architecture became less prevalent. Social conditions and laws altered considerably. These factors, coupled with the Great Plague, and the Great Fire of London, and the introduction of the use of bricks instead of stone, brought about a decline in operative masonry. This decline was so great, that by the late 17th century, freemasons became so few, that only a small number of lodges remained. During this period, referred to by Masonic historians as the Transition Period, a number of important citizens commenced to take an active interest in the ancient customs of the craft, and, although not operative masons, were admitted into lodges. Because of these circumstances, they were called accepted masons. At first, the number of accepted Masons was small. By the early part of the 18th century, however, they outnumbered the operatives, and exerted a great deal of influence on the expansion of Freemasonry, and on its principles of fellowship, and charitable pursuits.