Explorers and travelers have known of the pool by the great rock for centuries. A valuable water source and resting place, many who passed by inscribed their names and messages in the rock next to petroglyphs left by ancient Puebloans. The ruins of a large pueblo located on top of El Morro were vacated by the time the Spaniards arrived in the late 1500s, and its inhabitants may have moved to the nearby pueblos in Zuni and Acoma. As the American West grew in population, El Morro became a break along the trail for those passing through and a destination for sightseers. As the popularity of the area increased, so did the tradition of carving inscriptions on the rock. To preserve the historical importance of the area and initiate preservation efforts on the old inscriptions, El Morro was established as a national monument by a presidential proclamation on December 8, 1906.