Final answer:
The first Celtic cross is attributed to an ancient legend.
Step-by-step explanation:
The creation of the first Celtic cross by making the mark of a Latin cross through a circle on an ancient standing stone monument is attributed to an ancient legend.
However, it is important to note that the exact origin and creator of the first Celtic cross is not historically documented, and therefore remains a part of folklore and legend. This legend signifies the blending of pre-Christian Celtic beliefs with the introduction of Christianity.