sentences:  The Bastille was used to investigate and break up Protestant networks by imprisoning and questioning the more recalcitrant members of the community, in particular upper-class Calvinists; some 254 Protestants were imprisoned in the Bastille during Louis's reign.By Louis's reign, Bastille prisoners were detained using a "lettre de cachet", "a letter under royal seal", issued by the king and countersigned by a minister, ordering a named person to be held.Louis, closely involved in this aspect of government, personally decided who should be imprisoned at the Bastille.