In 590, a great plague struck Rome. Pope St. Gregory the Great led a procession through the streets as an act of penance, seeking the forgiveness of and atoning for sin. At the tomb of Hadrian (now Castle Sant’ Angelo near St. Peter’s Basilica), St. Michael appeared and sheathed his sword, indicating the end of the plague. More @Wikipedia
Hover over any link to get a description of the article. Please note that search keywords are sometimes hidden within the full article and don't appear in the description or title.