Gregorios 155 was a deacon; in 814 Gregorios 155 and Christophoros 56 were sent by the emperor Leo V (Leo 15) as envoys to Charlemagne (Karoulos 1), in company with Karoulos 1's envoys Amalarios 1 and Petros 141, with the agreed text of an alliance; on arrival they found that Karoulos 1 was dead and had been succeeded by Louis the Pious (Lodoïchos 2); they were received by Lodoïchos 2 and then dismissed with Lodoïchos 2's own envoys (Nordbert 1 and Richoin 1) sent to renew friendship with Leo 15 and ratify the agreed treaty: Annales Regni Francorum s.a. 814.

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