The coronation of David took place in late September or early October of 641, the new emperor being a ten-year-old boy. David assumed the name Tiberius upon his coronation. The adoption of one of the traditional
regnal names was common among seventh- and eighth-century Byzantine emperors: other examples include Apsimarus/
Tiberius III (698), Bardanes/
Philippicus (711), Artemius/
Anastasius (713), Basilius/
Tiberius (718), and Petasius/
Tiberius (728). The most important primary source for the period preceding the reign of Tiberius is
Nicephorus, but that account breaks off as Tiberius is crowned, leaving his short reign attested only by sparse and contradictory sources. One dubious source is the
Synodicon Vetus, where Tiberius is attested as the recipient of a papal letter: , Tiberius and
Constans II The editors of the 1979 edition of the
Synodicon Vetus, John M. Duffy and John Parker, note that the account becomes confused in this area, and the letter was more likely sent to ConstantineIII and Heraclonas.
Christological controversy was rife at this time, and Martina enthusiastically supported
Monothelitism.
Numismatists in the nineteenth century suggested that Tiberius was portrayed on certain copper coins, but these identifications were later shown to be mistaken. Some coins were presumably minted during his reign; Byzantine numismatist Wolfgang R. O. Hahn points out that mints sometimes resort to
type immobilisé, continuing to use old motifs even after the emperor depicted has already died or lost power. Since there were multiple emperors in 641, the mints may have resorted to reusing a depiction of three co-emperors originally intended to signify Heraclius, ConstantineIII and Heraclonas. Hahn points to a coin with this depiction which bears an
epsilon on its back, as well as the Heraclius monogram. One possibility is that the epsilon represents "ἕτερος", "the second", referring to "HeracliusII", meaning Heraclonas, whose name is a
diminutive of his birth name Heraclius, and that this three-emperor coin has been made to represent Heraclonas and his co-emperors, ConstansII and Tiberius. Alternatively, and with the same result, epsilon (the fifth letter of the Greek alphabet) could signify the fifth year of a
lustrum cycle, which here would apply to the 15th
indiction beginning on 1 September 641. Some fragmentary Egyptian papyrus documents from 641 contain dating clauses that scholars have taken to refer to David, giving the number of years since he was raised to
caesar. The
Muslim conquest of Egypt was ongoing at this time, which would end with the negotiated surrender of Egypt to the
Rashidun Caliphate. Martina and her sons took a relatively moderate stance toward the Muslims, likely out of fear that any intensification of the fighting would further jeopardize the regime. (orange, possessing
Anatolia,
North Africa, and much of Italy) in 650, showing the
Rashidun Caliphate (green, possessing Egypt,
the Levant, and much of
the Middle East), after the loss of Egypt and other territories to Muslim conquest == Downfall ==