reached an agreement but most probably the Frankish Emperor did not agree to any tangible actions. However, when the news for a possible alliance between the two empires reached Pliska, the Bulgarians decided to conclude a peace. Moreover, they needed to consolidate their authority in the newly conquered lands. The appearance of the Frankish state and the new stirring of the tribes in the steppes necessitated that the rear should be secured before further campaigning against the Byzantine Empire. Those considerations gave reason for Omurtag to conclude a 30-year peace treaty with the Byzantines in 815, which was partly inscribed on a surviving column found near the village of Seltsi, Shumen Province. According to that inscription the treaty specified: the border in Thrace. It began on the Black Sea coast near Debelt, passed along the earth ditch Erkesiya, continued to the Makri Livada (in modern Haskovo Province) on the Maritsa river and from there to the Rhodope mountains but without including Plovdiv within Bulgaria's borders. the issue with the Slavs which remained in Byzantium. The Bulgarians proposed to exchange the Byzantine captives for the Slavic population of Thrace. the exchange of the other prisoners of war. The two rulers had sworn to uphold the conditions of the treaty by each other's rites, which scandalized the Byzantine court. The treaty was very favourable for Bulgaria because the country needed peace. The army was exhausted, the capital Pliska was still in ruins after the invasion of Nicephorus I in 811 and the Byzantine Empire was no longer a serious threat for the Bulgarians. The treaty was honoured by both sides and was renewed after the accession of the new Byzantine Emperor Michael II to the throne in 820. In 821 Thomas the Slav rebelled against the Byzantine Emperor and laid siege to Constantinople to seize the Imperial throne for himself. Khan Omurtag sent an army to help Michael II put down the rebellion which attacked the rebels at the Battle of Kedouktos (winter 822 or spring 823). Relations with the Frankish Empire In 818 the Slavic tribes of the Timočani, Abodrites, and Braničevci (who inhabited the lands along the middle Danube, former Avar domains) rebelled against the increasingly centralized Bulgarian suzerainty in the west and sought the support of the Frankish Emperor Louis the Pious. Between 824 and 826 Omurtag approached the Frankish court with an attempt to seek a diplomatic resolution