In Poe's short story "The Masque of the Red Death," why does Prince Prospero lock himself and his guests inside his castle?

The prince thought that if he isolated himself from the plague running rampart throughout the countryside, he would be able to avoid contamination. He invited a select few to be part of his court to keep him company. Also, in that way he could "play king" and pretend that everything was normal. However, the "out of sight, out of mind" principle did not work, as Death came to his very door.

Check out the reference below for further insight into the multiple meanings of the mask in this regard.