The Cleveland Museum of Art has a corner post from a stone railing, carved in red sandstone at Mathura in northern India in the second century. It’s about eighty centimetres tall. A vine runs across the top, hung with what look like bunches of grapes. Under it, women play a lyre, a harp and castanets, and some of them seem to be drunk. At the foot of the post, on one face, a hunchbacked woman ladles wine from a big bowl for a fat seated man, a yaksha, one of the nature spirits.

Round the corner, on the next face, there’s a figure with a woman’s body and a horse’s head. She’s down on one knee with her arm out, reaching for a man who has his own arm up over his head. The museum says this “probably illustrates the story of the horse-headed yakshi who ate her victims.”

That’s a fair summary of the first part. The story is a jataka, one of the tales of the Buddha’s earlier lives, number 432 in the standard collection. A queen of Benares swore an oath she knew was false: if she was lying, she said, let her be reborn as a demon with a horse’s face. She was. After three years serving the demon king, she was given leave to eat any human who strayed into a certain stretch of country. One day she caught a young brahmin, and instead of eating him she fell in love with him. She kept him in a cave, and when she went out she rolled a stone across the mouth so he couldn’t leave.

They had a son, and this son is the one the story is about, because he’s the future Buddha. When he was old enough, he asked his mother how far her ground reached, and she told him. She named the landmarks and pointed out the space, thirty leagues by five. Then he moved the stone while she was away, and he and his father ran for the edge of it. She came after them and stopped where her ground stopped. She begged them to come back. They wouldn’t.

So she gave her son the only thing she had left to give. “Take, my child, this invaluable charm,” she says in the 1897 English translation: a charm that let him follow anyone’s footsteps, even twelve years after they’d been made. Then she died there at the boundary, of grief.

I keep coming back to what she gave him, and that she gave it twice. When he asked where her ground ended, she told him, landmark by landmark. That was all he needed to leave her. Then, at the line she couldn’t cross, she gave him what she couldn’t have herself: the power to follow anyone, anywhere.

The rest of the story barely remembers her. The son goes to work for the king of Benares. To test him, the king and his chaplain steal from their own treasury and hide the loot in a reservoir, and he tracks them, even through the air. “I see footsteps in the air,” he says. “Bring me a ladder.” The jataka is told to explain a seven-year-old boy in the Buddha’s own day who could read footprints. In this story she isn’t the point. She’s how the boy got his gift.

If that is her, the carver gave her the grab. That’s the right scene for a railing about wine and music. Wine-pouring, drunk musicians and a woman with a horse’s head who eats people all make a lively, slightly dangerous post. But anyone walking past who knew the story would have known how it ended. She doesn’t eat him. She falls in love with him, shows her son the way out, and dies at the edge of her ground.