The first chapel in Utrecht was founded around 630 by Frankish clergy under the patronage of the Merovingian kings but was destroyed during an attack of the Frisians on Utrecht shortly thereafter. The site of this first chapel within Utrecht is unknown. Saint Willibrord (died 739), the Apostle to the Frisians, established a second chapel devoted to Saint Martin on (or close to) the site of the current building. This church was destroyed by the Normans in the 9th century during one of their many raids on Utrecht, but was reconstructed by Bishop Balderic in the 10th century. During this period St. Martin's came to be the principal church of Utrecht, see of the bishop. The church had its own small territorial close (known as an "immunity") and was led by a cathedral chapter of canons, who generally belonged to the nobility.