Convents and monasteries were places of silence. The importance of silence was stressed in the cloister of San Marco, where the first image that greeted friars and visitors alike was Fra Angelico’s fresco of Peter of Verona with his finger to his lips. Silence was preserved in the cloisters, the church, and the dormitory. To keep the friars on their toes, each convent had an officer, the circator, whose job was to move quietly among the brothers “at odd and unexpected moments” to see if they were growing slack.

King, Ross (2012-10-30). Leonardo and the Last Supper (p. 60). Bloomsbury Publishing. Kindle Edition.