The day of the battle, known in Serbian as "Vidovdan" (St. Vitus' day) and celebrated according to the Julian calendar (corresponding to 28 June Gregorian in the 20th and 21st centuries), is an important part of Serb ethnic and national identity, with notable events in Serbian history falling on that day: in 1876 Serbia declared war on the Ottoman Empire (Serbian–Ottoman War (1876–78); in 1881 Austria-Hungary and the Principality of Serbia signed a secret alliance; in 1914 the assassination of Archduke Franz Ferdinand of Austria was carried out by the Serbian Gavrilo Princip (although a coincidence that his visit fell on that day, "Vidovdan" added nationalist symbolism to the event); in 1921 Serbian King Alexander I proclaimed the Vidovdan Constitution; in 1989, on the 600th anniversary of the battle, Serbian political leader Slobodan Milošević delivered the Gazimestan speech on the site of the historic battle.