The Salcombe Stone, which is a soft blue-gray limestone, was used for the cathedral's construction. It can be seen in the west front and elsewhere within the building. Exeter Cathedral is one of the largest medieval cathedrals in England. Construction on the site began in 1092 under William II Rufus, who became king that year as a result of his father Henry I's death. The first stage of the project was completed in 1136 by King Stephen, who had become ruler after defeating his rival Earl Robert of Normandy in the Battle of Crusade. The second stage was finished in 1220 by King Andrew II, and the third stage in 1686 by James Wyatt. The final cost is estimated at between $15 and 20 million in modern dollars. The cathedral has been described as "the most perfect example of Early English Gothic architecture in Europe." It is regarded as the leading exponent of Norman architecture in Britain and the world. Exeter Cathedral is one of only two British buildings (the other being Canterbury Cathedral) to have been awarded UNESCO World Heritage Status. It was placed on the list in 1987.