Americans are observing Memorial Day weekend, a time meant to honor the nation's war dead, with ceremonies, parades, sporting events and picnics.

The last Monday in May of each year is designated as Memorial Day, a time to place flowers on military gravesites and honor the U.S. servicemen and women who gave their lives in service of the country.

At Arlington National Cemetery near Washington and many other national cemeteries, volunteers place a small American flag on every military grave. Thousands of motorcycle riders from a nationwide group called "Rolling Thunder" stage a ceremonial ride into the nation's capital, to call attention to veterans' issues and to remember service members who went missing in action.

Defense Secretary Robert Gates and military Joints Chiefs' chairman Admiral Mike Mullen are scheduled to speak to the group.

Public television and radio will broadcast a Sunday evening concert from the National Mall featuring retired Army General and former Secretary of State Colin Powell as well as other prominent public figures.

Ceremonies also will be held at several of the war memorials in the nation's capital and around the country.

Because many people have the day off from work on Memorial Day, the long weekend is seen as the unofficial start of the summer vacation season, celebrated with picnics and weekend trips to the beach, a park or a campground. Some Americans say they are concerned that the day has become more of a recreational holiday than a time to reflect and honor the dead.