 A fervent Catholic, he played an important role in the history of Jansenism and was one of the Solitaires of Port-Royal-des-Champs.He was also renowned for his part in the development of the pruning of fruit trees, to which he was devoted.Robert Arnauld was born in Paris, the eldest of the twenty children of lawyer Antoine Arnauld, procurator-general of Catherine de Médicis, and his wife Catherine Marion.