The Greek Prophetologion manuscript Q12 from the library of the Academy of Sciences in St. Petersburg, copied in 1275, contains some thirty marginal notes written in Alanic, a pre-stage of Ossetic. On leaf 100r, the glossator provided the Greek heading τ παραμο(ν) τς μέ(σο) ν´ (i.e. μεσοπεντηκοστς), ‘Eve of Mid-Pentecost’, with a gloss πητζινάκ χουτζάου πάν which most probably means ‘Pecheneg Sunday’. A Pecheneg festival established after the decisive victory of John II over the Pechenegs is attested by both Nicetas (...) Choniates and Ecloga Basilicorum. It is no wonder that this festival reached distant Alania, since the 12th century was a heyday for the Orthodox Christianity in the Northern Caucasus. The battle took place near Beroea in spring of the “fifth year” of John II's reign. The majority of historians tend to opt for 1122, but we would not exclude 1123 either. Whatever the year, the marginal note from Q12 may help in establishing the day of the battle, which is not mentioned either in Greek or in Scandinavian sources. If the battle of Beroea took place in 1122, it happened either on the 20th–22nd or on the 24th–26th of April. If the battle was fought in 1123, the day of the victory could then be either the 10th–12th or the 14th–16th of May. (shrink)