Bad Hersfeld's written history begins with the monk Sturm, who established a monastic settlement in "Haerulfisfeld" but later evacuated it to Fulda, and with Lullus, who reëstablished the Benedictine Hersfeld Abbey in 769. Both had been missionary bishop Boniface's disciples. The monastery was enlarged between 831 and 850 and Lullus's remains were moved in 852 to another grave in the new basilica. During this ceremony his canonisation was announced by Rabanus Maurus. Since 852, the "Lullusfest", the oldest folk festival in Germany, has been celebrated in the week of Saint Lullus's day, 16 October (his day of death). Martin Luther visited the monastery, on his way back from the Diet of Worms in 1521 and held a sermon in the abbey church on 1 May. About two years later, the town and the territory of the abbey was mostly Protestant.