Pechenegs raiding the Chersonnesos were defeated by Ioannes Bryennios & became his allies

Summary:
Ioannes Bryennios used a Pecheneg attack as an excuse for his retreat from the failed siege of Constantinople. He led his troops against them, defeated them and subsequently a treaty was agreed with an exchange of hostages. This secured Pecheneg support for the rebellion of Ioannes' brother Nikephoros 
Dates:
1078 
Ioannes Bryennios, brother of usurper Nikephoros (Ioannes 61)
  • Using as a pretext the announced Pecheneg attack he raised the siege (of Constantinople), marched against them, encountered them on their return, defeated them completely, killed many, captured great numbers and returned to his brother (Nikephoros 62) (:) ἀπαγγέλλεταί τι πλῆθος Σκυθῶν διαβὰν τὸν Αἷμον καὶ τὰ κατὰ τὴν Χερρόνησον κατατρέχον χωρία καὶ ληϊζόμενον. Τοῦτο τοίνυν ἀφορμὴν εὑρὼν ὁ στρατάρχης λύει τὴν πολιορκίαν Bryennios 237.8-12
Nikephoros Bryennios usurper [1077] (Nikephoros 62)
  • Acquired allies among the Pechenegs with whom peace and a treaty were established after the exchange of hostages following their defeat by his brother (Ioannes 61 Bryennios) (:) Γίνονται οὖν οἱ ἑαλωκότες ἐκείνῳ ἀφορμὴ πρὸς τοὺς Σκύθας εἰρήνης τε καὶ ξυμβάσεως· ὁμήρους γὰρ τῶν ἐπιφανῶν δόντες τούς τε οἰκείους αἰχμαλώτους εἰλήφασι καὶ σύμμαχοι τούτῳ κατέστησαν Bryennios 237.13-14