A memory palace (or memory crossing) was a highly complex form of mental visualization that Aloysius Pendergast trained himself to do. It combined Tibetan meditation techniques from the Chongg Ran discipline with concepts Pendergast found in a sixteenth-century Italian manuscript by Giordano Bruno titled Ars Memoria, Art of Memory.
The technique allowed him to combine all the facts and intitutions about a topic and turn it into a three-dimensional scene. After creating a memory palace, Pendergast could visualize a memory or a historical event in his mind as if he were actually there.
Creating a memory palace was mentally draining and required much preparation on Pendergast's part. He began by laying very still for several minutes, arranging facts in his mind. He then shut out all external stimuli, including his own inner monologue. He solved complex mathematical equations in his head, simulating a game of bridge with four players, and one by one his senses faded away until finally the memory palace faded into being.
Pendergast has used the technique several times in the course of his investigations, including:
- In The Cabinet of Curiosities, to visualize J.C. Shottum's Cabinet of Natural Productions and Curiosities and certain areas of lower Manhattan (including the Five Points neighborhood) in 1881
- He sometimes used it to remember conversations and events in his childhood home of Rochenoire