Local people in the Theme of Bulgaria rebel against the Empire in during the summer of 1040.

The uprising spreads and the rebels very quickly take over control over northern part of Pomoravlje and liberate Belgrade.

The origins of Peter Delyan are not clear.

He claims that he is a son of emperor Gavril Radomir and grandson of Samuel of Bulgaria, but he could also have been local who became the leader of an uprising against Constantinople’s rule over Bulgaria and claimed to be Samuel's grandson to justify his proclamation as Tsar Peter II of Bulgaria in Belgrade in 1040.

He is soon joined as co-ruler by Prince Alusian, a member of the ruling family, and leads Bulgarian forces in an open rebellion against Constantinople’s rule in a bid for independence.