By the 9th century, Croats have already been fully included in a large European Christian community. Croatian rulers Mislav (around 839), Trpimir I (852) and many others were building churches and monasteries. In 879, Croatian duke Branimir wrote a letter to Pope John VIII in which he promised him loyalty and obedience. Pope John VIII replied with a letter on 7 June 879, in which he wrote that he celebrated a Mass at the tomb of St Peter on which he invoked God's blessing on Branimir and his people.