Placidus was a 3rd-century Roman priest and monk from Trasacco who is venerated as a saint and hieromartyr. According to historical records, he lived during the era of Roman persecutions and was martyred alongside other Christians, including the priest Cesidius, under the orders of Emperor Maximinus Thrax. While later legends erroneously linked him to the disciples of Benedict of Nursia, historical evidence suggests his martyrdom occurred in the Marsi region during a period of intense religious conflict.