After returning from their crusades to Jerusalem, the Knights Templar built this stronghold in 1240 to serve as the headquarters of the Order in Europe and the center of its charitable works. After King Philip IV betrayed the Order and executed Jacques de Molay, the Temple was used for a time by the Knights of Malta before being converted into a prison. Most of the French royal family were held within its walls, most notable Louis XVI, Marie Antoinette, and the daupin, Louis-Charles.*
* Now that would have made for a great reality TV show. Just add a public vote and some kind of eviction party in front of a jeering crowd. They could even yell "Cut!" as the guillotine fell.
By the early 1800s, the prison had become a place of pilgrimage for royalists, and Napoleon ordered it demolished to remove its use as a symbol of the old monarchy. Today, it survives only as a stop on the Paris Metro and a covered market in the third arrondissement, its name a silent memorial to a betrayer king and a king betrayed.