A palindrome is a word, phrase, number, or other sequence of units that may be read the same way in either direction, with general allowances for adjustments to punctuation and word dividers. Composing literature in palindromes is an example of constrained writing. The word "palindrome" was coined from the Greek roots palin (palin; "again") and dromos (dromos; "way, direction") by the English writer Ben Jonson in the 17th century. The Greek phrase to describe the phenomenon is karkinike epigrafe (karkinik_ epigrafh; "crab inscription"), or simply karkinoi (karkinoi; "crabs"), alluding to the movement of crabs, such as an inscription that may be read backwards. Palindromes date back at least to 79 AD, as a palindrome was found as a graffito at Herculaneum, a city buried by ash in that year. This palindrome, called the Sator Square, consists of an entire sentence written in Latin: "Sator Arepo Tenet Opera Rotas" ("The sower Arepo holds works wheels").
Contributions by 184.108.40.206, 220.127.116.11, and 18.104.22.168.