The Polish Cavalier

With the help of special armor, a singing sword, and a magnificent horse, a 15 year old boy saves Poland from an invasion by 10,000 Mongol horsemen.
In present day Poland a trumpeter appears every hour in a tower of St. Mary's Cathedral in Krakow and sounds an alarm which is abruptly halted, signifying when a Tartar arrow strikes him in the throat in 1341. This is the approximate time of when this story takes place.