Ancient Egypt²,³
Despite the belief that nudity has always been questioned, several modern naturist principles actually originate from ancient civilizations. During the first Ancient Egyptian dynasties, the nobility attempted to use clothing to differentiate themselves from the lower classes. Nudity was normalized from birth among the lower classes, with children normally nude until puberty and adults nude while they worked. For nobles on the other hand, being naked, especially while carrying out their duties, would be considered dropping to the level of the lower classes, therefore it was far less common.
However, some of the most famous figures of Egyptian history dared to go against these beliefs. In 1887, in a small town in the Nile Delta, clay tablets were discovered with inscriptions that spoke of nudity as a form of Sun worship. Once translated, the inscriptions revealed that the controversial Pharaoh Akhenaten (1385-1353 B.C.) and Queen Nefertiti considered that the sun, Aton, was the true source of life. Therefore, they sunbathed nude to achieve physical and spiritual development and to connect with Aton at a higher level. This then progressed to being nude more often in their private quarters.
Although their nude practice was initially a way to find enlightenment, it seems as though they also became more comfortable with their bodies, which went against the commonly held attitudes of Egyptian nobility. Egyptians from the lower classes up to Akhenaton and Nefertiti found a way to normalize and own their lifestyle, a valuable lesson that remains a naturist principle today.
²Ogden Goelet "Nudity in Ancient Egypt". Source. Volume 12, Number 2. 1993
³Goodson, A. (1991): Therapy, Nudity & Joy: The Therapeutic Use of Nudity Through the Ages, from Ancient Ritual to Modern Psychology. Elysium Growth Press.