M-113 was a desolate planet that was once home to an ancient civilization, as well as the homeworld of an indigenous species known as the M-113 creature or "salt vampire".
The planet was hotter and more arid than Earth, so Human inhabitants needed to ingest larger amounts of salt to adjust for the loss of the mineral due to sweating. No salt was found on the planet so it had to be imported. Apart from dry brushes, it was home to a poisonous plant, the Borgia plant, classified as a carbon group 3 vegetation, similar to Earth's nightshade family.
A winged beast
Several stone sculptures depicting various animals were found on the surface of the planet among vast ruins, including sculptures of a winged creature holding a sword, a small stone sculpture resembling a dolphin as depicted in Earth's Renaissance, a four-legged deer-like creature seated like a traditional Egyptian sphinx statue and a sculpture of a lion-like animal.
In 2261, archaeologist Robert Crater and his wife Nancy began an expedition on M-113 to conduct a survey of the planet's many ruins. They moved into a large deserted ruin on the planet surface and began their archaeological research. During the first four years, they shipped out large amounts of artifacts, gathered from several digging sites on the planet, made numerous reports and were visited by a number of ships. A large drop in shipments was noted in the fifth year, however.
Unknown at the time of the Crater expedition, a single surviving member of the "salt vampire" species continued to live on the planet. It eventually killed Nancy and continued to live along with Robert until 2266. Crater buried his wife on a hill on the planet, but was no longer as efficient in his archaeological work, causing the drop in shipments. (TOS: "The Man Trap")