The Monument of Unification in Plovdiv was created in 1985 in honour of the 100th anniversary of the Unification of Eastern Rumelia and the Principality of Bulgaria in 1885. Every year on September 6th the historical event of the Unification is noted as an official holiday in Bulgaria and a Day of Plovdiv with a solemn ceremony in the square in front of the Monument.

This event is one of the most important in the historical development of Bulgaria. After the Russo-Turkish war for the liberation of Bulgaria from Ottoman rule, the Berlin Peace Treaty of 1878 divided Bulgaria into two independent parts (states). The northern half was the Principality of Bulgaria with Sofia as capital and the southern (Eastern Rumelia) with the capital being Plovdiv.