Kubrat spent his early life at the
Byzantine Empire imperial palace in
Constantinople. As the 7th-century Byzantine historian
John of Nikiu narrates: Whether he was a child or a young adult during his time in Constantinople is unclear. The exact time of this event is also unknown but probably coincided with the reign of Emperor
Heraclius (r. 610–641). His or Organa's conversion to
Christianity is placed circa 619 AD. It seems that young Kubrat was part of the pre-planned coalition, initiated by Heraclius or Organa, against the Sasanian–Avar alliance. This coincides with other alliances by Heraclius with steppe peoples, all in the interest of saving Constantinople. Kubrat, in 635, according to
Nikephoros I, "ruler of the
Onoğundur–Bulğars, successfully revolted against the
Avars and concluded a treaty with Heraclius". The state
Old Great Bulgaria (Magna Bulgaria) was formed. Kubrat died "when Konstantinos was in the West", somewhere during the reign of
Constans II (641–668). According to Nikephoros I, Kubrat instructed his five sons (
Batbayan,
Kotrag,
Asparukh, two others unmentioned are considered to be
Kuber and
Alcek) to "never separate their place of dwelling from one another, so that by being in concordance with one another, their power might thrive". However, the loose tribal union broke up under internal tensions and especially
Khazars pressure from the East. == Kubrat's death ==