Trondheim's cathedral was built on the grave of King Olav, who formulated a Christian religious code for Norway in 1024. The town quickly became a pilgrimage site for Christians from all over Northern Europe, and Olav was canonized in 1164. Construction of Nidarosdomen began in 1070, but the oldest existing parts of the cathedral date from around 1150. It has been ravaged on several occasions by fire and rebuilt each time, generally in a Gothic style. Since the Middle Ages, Norway's kings have been crowned and blessed in the cathedral. The crown jewels are on display here. Forty-five-minute guided tours are offered in English from mid-June to mid-August.