O Arco de Sant'Ana is a historical novel written by Almeida Garrett. In the 14th century, it took place in the shadow of the arch of the same name on Rua de Santana in old Porto, on the way to the Cathedral. In the time when the Bishop of Porto was king and lord of his feud, he allowed himself, after an attempt to seduce the young mother, Aninhas, whose husband, Afonso, was absent, to have her kidnapped by his henchmen headed by the chief of guard Pêro Cão. The neighbor friend Gertrude, the girlfriend of the bishop's protégé, the young student Vasco, gives the alarm and orders him to seek help from el-rei D. Pedro. The young man went, in his sorrel, to Gaia, where the witch Guiomar, who will come to be known as his mother, who conceived him on a night of terrible memory, was abused by the current bishop. Then, a knight who had been wounded in the civil war and had been collected on death's doors and treated by the father of Jewish Guiomar, the physicist Abraão Zacuto. The people revolted and surrounded the episcopal palace to demand the release of Aninhas. Vasco was ahead of the contenders, and then it revealed that the bishop was his parent.
In the meantime, the king emerges from the crowd. He also imposes his justice with the whip, expelling the unworthy bishop from the kingdom. Pêro Cão found hanging from a sterile fig tree. D. Pedro sponsors Vasco and Gertrude's wedding. Afonso returns home and promises not to leave the beautiful Aninhas alone.