Why is a cannon fired every day at noon in St Petersburg

Every day, a loud volley from a signal cannon sounds in the city center. What's behind this ancient tradition and who invented it?

St. Petersburg, Russia's northern and (still) cultural capital, is very proud of its history. Great care is taken to preserve the historical center and customs that date back to tsarist times.

"One of St. Petersburg's traditions is the firing of a signal cannon at midday from th