What is mary on a cross about?

There's no widely known or established figure or story called "Mary on a Cross." The phrase itself is unusual. Mary, the mother of Jesus, is depicted in Christian art and tradition in many ways, but not typically on a cross herself. She is often shown at the foot of the cross, grieving the crucifixion of her son.

It's possible you're:

• Misremembering a detail: Perhaps you're thinking of a specific artwork or story that features Mary in a scene related to the crucifixion, but the phrasing is slightly inaccurate.
• Referring to a lesser-known piece of religious art or literature: There might be obscure depictions or interpretations that use imagery involving Mary and a cross in a less conventional way.
• Confusing with another story or figure: There might be a different narrative or character that involves a "Mary" figure and a cross that you're remembering.

To provide more information, please clarify your source or provide more context about where you encountered this phrase.