The former church of Saint-Jacques-la-Boucherie (Saint James of the butchery), built between 1509 and 1523 to welcome pilgrims setting out on the road to Tours, headed on the pilgrimage route (see my Northern Spain trip on the end of the pilgrimage route later in this blog). The church itself was was demolished in 1797, then the tower, which is all that remains, purchased by the City of Paris in 1836.
The tower has recently been cleaned and restored to its former glory.
The Tower houses a statue of Blaise Pascal, French mathematician, physicist and religious philosopher, commemorating experiments he conducted on atmospheric pressure here. Nicholas Flamel (familiar to readers of the Harry Potter books as the alchemist who created the sorcerer's stone) was a patron of the church and is buried under the Tower floor: