The French authorities are on high alert for a terrorist attack.
Béatrice Lagarde, the local prefect, said: "The terrorist threat remains high in France and even though Lourdes has never been targeted by radical Islamists, a terrorist attack is a possibility we cannot ignore."
Sniffer dogs and bomb disposal experts have also been deployed to the religious site and pilgrims will be subject to security checks and bag searches upon entering the secured site.
On the day that the Catholic Church, Eastern Orthodoxy, Oriental Orthodoxy, and parts of Anglicanism, believe Mary was taken into Heaven at the end of her earthly life, around 25,000 pilgrims are expected to visit Lourdes in South France.
Lourdes marks the town in which Catholics believe Mary appeared in a vision to Bernadette Soubirous.
The Catholic Church has recognised 69 official healings in the spring waters from the grotto.