Fifth Avenue was a sea of green Thursday as the city celebrated Irish heritage at the 250th St. Patrick's Day Parade.

Best-selling author Mary Higgins Clark was grand marshal in the parade that began at 44th Street and Fifth Avenue, amid pleasant temps that were expected to reach the low 60s.

Check out our feature page for all things St. Patrick's Day.

Mayor Michael Bloomberg attended Mass at St. Patrick's Cathedral before marching in the parade.

Paradegoers gave him a warmer welcome on Fifth Avenue than he got at a St Patrick's Day parade recently in Queens. Some were angry about the mayor's joke last month about seeing  "people that are totally inebriated" at the American Irish Historical Society in Manhattan. Bloomberg apologized shortly after making the comment.

There weren't many boos for the mayor on Thursday, and many said they had not even heard of the remark. The parade draws enthusiasts from all over the world.

New York City's parade was first marched in 1762 -- 14 years before the Declaration of Independence was signed.

The day is named after St. Patrick, who introduced Christianity to Ireland about 1,500 years ago and became the country's patron saint.

He was born in Britain to an aristocratic Christian family, according to classics professor Philip Freeman of Luther College in Iowa, who authored the book "St. Patrick of Ireland: A Biography.

At 16, Patrick is said to have been kidnapped and sent to then pagan Ireland to tend sheep. He was eventually ordained a priest and spent the rest of his life converting the Irish to Christianity.