British, Belgian royals join relatives of fallen to mark bloody battle's centenary

YPRES, Belgium - Britain's Prince William and his wife, Kate, on Sunday joined Belgian royals and relatives of soldiers who fought in the Battle of Passchendaele to mark 100 years since the offensive that became a symbol of war's senselessness began.

More than half a million Allied and German troops were killed or wounded in the World War I battle in western Belgium, also known as the Third Battle of Ypres.

The Allied campaign, fought by British and Commonwealth forces from July to November 1917 in swampy, rain-pummeled battlefields that turned to liquid mud, ended up barely moving the front line against the Germans.