The importance placed on Greek fire during the Empire's struggle against the Arabs would lead to its discovery being ascribed to divine intervention. The Emperor Constantine Porphyrogennetos (), in his book "De Administrando Imperio", admonishes his son and heir, Romanos II (), to never reveal the secrets of its composition, as it was "shown and revealed by an angel to the great and holy first Christian emperor Constantine" and that the angel bound him "not to prepare this fire but for Christians, and only in the imperial city." As a warning, he adds that one official, who was bribed into handing some of it over to the Empire's enemies, was struck down by a "flame from heaven" as he was about to enter a church. As the latter incident demonstrates, the Byzantines could not avoid capture of their precious secret weapon: the Arabs captured at least one fireship intact in 827, and the Bulgars captured several "siphōn"s and much of the substance itself in 812/814. This, however, was apparently not enough to allow their enemies to copy it (see below). The Arabs, for instance, employed a variety of incendiary substances similar to the Byzantine weapon, but they were never able to copy the Byzantine method of deployment by "siphōn", and used catapults and grenades instead.