The Saint-Jacques tower stands alone in the middle of a little garden that bears its name.

A tower in the flamboyant Gothic style, built between 1509 and 1523, the Saint-Jacques tower is the only remaining vestige of the Saint-Jacques-de-la-Boucherie church built in 1797. This sanctuary was the departure point on the Via Toronensis (or Tours way) of the pilgrimage route to Saint-Jacques-de-Compostelle (Santiago de Compostella) in Spain. The statue of Blaise Pascal, at the base of the tower, is a reminder that it was here that he repeated his barometric experiments carried out in Puy-de-Dôme.

On the north-west corner, a statue of Saint Jacques le Majeur dominates the platform on which a small meteorological station has been installed since 1891. It belongs to the Observatoire de Montsouris. The sculpted symbols of the four evangelists (the lion, bull, eagle and man), appear in the corners. These statues were restored last century, along with the gargoyles and the eighteen statues of saints that decorate the walls of the tower.