The theta nigrum (lit. 'black theta') or theta infelix (lit. 'unlucky theta') is a symbol of death in Greek and Latin epigraphy.[1] Isidore of Seville notes the letter was appended after the name of a deceased soldier and finds of papyri containing military records have confirmed this use.[1] Additionally it can be seen in the Gladiator Mosaic.
The term theta nigrum was coined by Theodor Mommsen. It consists of a circle with a diagonal line. The theta signified Thanatos, the Greek deity of death.[2]
Nigrum præfigere theta; nam theta, Θ, præfigere, sumitur pro damnare, apud Persium: Et potis es vitio nigrum præfigere theta; (quippe theta, Θ, apud Græcos prima litera est nominis, Θάνατος, mors [...]