The Square René-Viviani - Montebello, created in 1928, is located north and around Saint-Julien-le-Pauvre church, opposite Notre-Dame. It is named after the French lawyer and politician René Viviani, (who was responsible for introducing the income tax in France, and who died in 1925), and after the nearby Montebello embankment.
What's specific about this square is the black locust (Robinia pseudoacacia) planted in 1601 by botanist Jean Robin who introduced the species in France. This tree is thought to be the oldest of Paris.
Source : translated from Wikipedia contributors, "Square René-Viviani - Montebello"