From the confines of Jerusalem and the city of Constantinople a horrible tale has gone forth and very frequently has been brought to our ears, namely, that a race from the kingdom of the Persians, an accursed race, a race utterly alienated from God, a generation forsooth which has not directed its heart and has not entrusted its spirit to God, has invaded the lands of those Christians and has depopulated them by the sword, pillage and fire; it has led away a part of the captives into its own country, and a part it has destroyed by cruel tortures; it has either entirely destroyed the churches of God or appropriated them for the rites of its own religion. They destroy the altars, after having defiled them with their uncleanness.
What historical event is the writer above referring to?