The deployment comes after a string of deadly attacks in Paris, Brussels, Nice and Munich in which over 250 people have died since January 2015.
- No skimping on security -
As head of the Roman Catholic church, Pope Francis is an important potential target.
The attempted assassination of pope John Paul II by Turkish gunman Mehmet Ali Agca on May 13, 1981, demonstrated that pontiffs are as vulnerable to assassins as politicians.
Warsaw has not skimped on personnel: 20,000 thousand policemen, including 7,500 patrolling the streets, 9,000 firefighters, and 800 special government agents as well as 1,000 border guards will be at work to ensure safety.
- Border checkpoints -
Border controls with EU neighbours have also been restored temporarily, while all small border traffic with non-EU Ukraine and the Russian exclave of Kaliningrad has been suspended.
Border guards have been banned from going on holiday and mobile checkpoints deployed to border points that were abandoned when Poland joined the visa-free Schengen travel zone in 2008.
Security has also been beefed up in areas the pontiff will visit, including a sprawling meadow in Brzegi, a village outside Krakow where a vigil will wind down the week-long WYD on July 30.
- ID required -
A huge metal fence has been thrown up around the site and anyone wanting to get in will require the right ID.
Firefighters will monitor Krakow's Balice airport, which Pope Francis will use for arrival and departure ,as well as train stations and bus stops used by participants.
Warsaw has refused to disclose how much the security operation is costing, but a special pool set aside in the 2016 budget for such events amounted to nearly 23 million euros ($25 million).