Editing Third Crusade (section)

===Conflict with Byzantium===
Lectoforus met the army at Pazardzhik and informed Frederick of the disrespect shown to his envoys. On 24 August, the imperial army reached [[Plovdiv|Philippopolis]], the Byzantine forces in the area having fled at their approach. On 25 August, Lectoforus' report was confirmed: Hermann of Münster, Rupert of Nassau, Henry of Dietz and Markward von Neuenburg had been stripped of their possessions and openly mocked in presence of the Ayyubid ambassador. That same day, a Byzantine envoy, James of Pisa, arrived with a letter from Isaac, who referred to Frederick as "king of Germany", refusing him the imperial title, and accused him of plotting to put his son Frederick on the throne of Constantinople. He nonetheless offered to fulfill the agreement of December 1188 to ferry the crusaders across the [[Dardanelles]] if he received hostages (including Duke Frederick and six bishops) in addition to the envoys he had arrested. Frederick's response that he would consider the offer only after the envoys were released.{{sfn|Freed|2016|pp=494–495}}

According to the ''History of the Expedition'', the receipt of Isaac's letter marked a break in crusader–Byzantine relations. Thereafter, the crusaders resorted to plunder and a scorched earth policy. On 26 August, the crusaders seized Philippopolis and its plentiful supplies. Frederick tried to communicate with the nearest Byzantine commander, the ''[[protostrator]]'' [[Manuel Kamytzes]]. When he received no response, he attacked his army on 29 August, killing fifty. The following day (30 August) or a week later (6 September), Duke Frederick and Duke Berthold occupied [[Stara Zagora|Berrhoe]] unopposed. Henry of Kalden occupied a castle called Scribention, while Bishop Diepold and Duke Berthold took a further two towns and ten castles. At this point, the local [[Armenians|Armenian]] and [[Bulgars|Bulgarian]] population swore oaths to Frederick to supply the market in Philippopolis as long as the crusaders stayed. They remained there and in partial occupation of Macedonia until 5 November.{{sfn|Freed|2016|pp=494–495}}

Isaac ordered Kamytzes to shadow the crusaders and harass their foraging parties.{{sfn|Magoulias|1984|p=222}} About 22 November 1189, with some 2,000 horsemen, Kamytzes set up an ambush for the crusaders' supply train near Philippopolis. The crusaders were informed of this from the Armenian inhabitants of the fortress of [[Prousenos]], where Kamytzes had set up his main camp. They set out with 5,000 cavalry to attack the Byzantine camp. The two forces met by accident near Prousenos, and in the ensuing battle, Kamytzes was routed. The historian [[Niketas Choniates]], who was an eyewitness, writes that the Byzantines fled as far as [[Ohrid]], and that Kamytzes did not rejoin his men until three days after the battle.{{sfn|Magoulias|1984|pp=224–225}}