They are called Teste di Moro because they are linked to a love story and tale of revenge between a young Sicilian girl and a young Moor:
Around the year 1,000, during the domination of the Moors in Sicily, a young girl peacefully passes her days in Palermo, spending much of her time on her balcony. One day she is noticed by a young Moor, who wastes no time in declaring his love for her. The young girl accepts and returns her courter’s feelings.
However the Moor has failed to reveal to her that he has a wife and children waiting for him in the east. When the young girl discovers the truth she feels betrayed and becomes so angry that she decides to take revenge. Waiting for his moment of maximum vulnerability, at night while he obliviously sleeps, she kills the Moor. Deciding that his face should stay at her side forever, she cuts off his head, makes a vase out of it and plants a basil seedling in it. So despite the terrible deed the girl is able to continue to take care of her beloved.
She places the head on her balcony and tends daily for the basil growing in it. Her neighbours, smelling the perfume of the basil and looking enviously at this vigorous plant in that unusual vase in the shape of a Moor’s head, get copies made for themselves of the one so lovingly tended by the young girl.