The Plongeons undertook the first excavation of Chichen Itza in 1875, and based their theories about Queen Moo on the murals and inscriptions that they found there.
Plongeon claimed that the Egyptian Sphinx, with its cat body and human head, was built by Queen Moo to honor her dead husband.
"[7] Evans explains that the meaning of the mural is still a mystery to modern scholars, but it may depict the ninth century sacking of the Mayan city, Piedras Negras.
[11] However, she argues that "two Aztec chacmools found in the context of the Templo Mayor bear more iconographic data, and it is those two which may resolve the identification of the figure.
In addition to Le Plongeon's belief that the Mayan culture was the foundation of Egyptian civilization, he also claimed that Free Masonry was invented by the Maya.
He did contribute a great deal of archaeological data in the form of photographs and molds of ruins and artifacts from Uxmal and Chichen Itza.
Not a single point of contact between the old and new worlds before the Columbian era can be proved by monuments or facts so far found in Yucatan or adjoining provinces.
Brian M. Fagan, professor of Anthropology and author, opined that Le Plongeon's theories "welled up from [his] romantic subconscious.
"[18] Evans writes that Le Plongeon's indulgence in psychic archaeology "dovetail[ed] neatly with his wife's profound interest mesmerism, seances, and the occult.
He had read the writings of Abbé Charles Étienne Brasseur de Bourbourg, a French writer, historian and archaeologist, about the diffusion of the Mayans to the Old World, and Le Plongeon was convinced of this theory before he even began his excavations.
Robert Brunhouse wrote in his 1973 book, In Search of the Maya, that Le Plongeon was "opinionated, haphazardly informed and reckless.
Codex Maya by Steve Benzell is a fictional adventure novel based on the character of Monique Le Plongeon who discovers a lost trove of Mayan codices.