Maris Cristallus was most likely a sea in which the Archipelago Ridiculus was found. This sea was supposedly explored by Gilderoy Lockhart who wrote about his "adventure" in Travels with Trolls. This expedition was, however a feat stolen by Lockhart from another wizard, whose memory was erased. Maris Cristallus was included on the map featured on the cover of Travels with Trolls.
- "Mare maris" means "sea" in Latin. Cristallus is presumably a derivation of the English adjective "crystaline", and together seem like "Crystaline Sea".
- Harry Potter and the Chamber of Secrets (film) (First mentioned)