Battle of Kosovo - a great event, a tactical victory of Ottomans and strategic victory of Serbians, the battle between Sultan Murad the first and prince Lazar, both of whom died in it, the fight that both left Balkan principalities bloodless and powerless, and prevented further expansion for time

... Truly underrated moment in European history that happened on 28th June 1389 year... Wait? Really?

Well, obviously we use Grigorian calendar, which was unexistent in 14th century... So, if we have to use a truly correct date, we should talk of 15th June instead... 28-13= 15. It seems as normal, so 28 still is valid date? NO! The problem is that before the Gregorian Calendar was created in 1582 (as many people forget), to turn dates into more "fitting ones", and here is a problem. Gregorian and Julian calendars use different systems of counting leap years. That's why instead of adding 13 to the Julian date we have to add just 8. That's how 28 turns into 23...

But "strangely", people don't care, and celebrate the jubilees on 28th!