In 1040,
Petar Delyan, who claimed to be a descendant of
Samuil of Bulgaria escaped from
Constantinople and began roaming throughout the Bulgarian lands, eventually reaching
Morava and
Belgrade. The rebellion broke out in Belgrade, where Delyan was proclaimed emperor of Bulgaria assuming the name of the sainted Emperor
Petar I. The Bulgarians moved southwards towards the last political centres of their empire,
Ohrid and
Skopje. On their way the local population joined them, accepted Petar Delyan as emperor and killed every Byzantine they met. In the same time local Bulgarians from the
Dyrrhachium area gathered around the soldier
Tihomir and headed westwards to reach the old capitals. The existence of two separate rebel camps became an actual threat for the success of the rebellion. Petar Delyan wrote a letter to Tihomir to negotiate for joint actions and asked that they should choose only one leader, either him or Tihomir. As he had greater influence than his rival, Delyan was unanimously chosen as leader and Tihomir was killed.With his enlarged army Petar II advanced to the south, surprised and defeated the Byzantine Emperor
Michael IV the Paphlagonian at
Thessaloniki. One of Michael's commanders the Bulgarian
Manuel Ivats, probably a son of Samuil's
boyar Ivats joined Petar II. After the victory the Bulgarian troops under the
voivoda Kavkan captured Dyrrachium on the
Adriatic Sea and some forces penetrated deep into
Thessaly eventually reaching
Corinth,
Epirus and most of
Macedonia were conquered. Another Bulgarian army led by Antim marched deep to the south and defeated the Byzantine commander Alakaseus in the battle of Thebes in
Boeotia. Upon the news of the Bulgarian success the Byzantine population of
Athens and
Piraeus who were uneasy due to the heavy taxes also revolted but were quickly crushed by
Norman mercenaries. The decisive actions of the rebels caused serious anxiety in Constantinople where plans for crushing the rebellion were hastily discussed. ==Arrival of Alusian==