Begun around 1503, which painting has been called the most famous portrait in art history?

Begun around 5,000 years ago, Stonehenge's construction belongs to which "New Stone Age" period? Which company, begun by a retired minister in 1876 to make socks for lumberjacks, soon expanded into underwear? Which war began with Frederick the Great's invasion of Saxony and lasted from 1756 to 1763? Begun in 1173, the Leaning Tower of Pisa is clad mainly in what stone? Begun in 1815, America's first large-scale monument to which man towers above Mount Vernon Place in Baltimore? Begun in 1845 and published in 1862, which Victor Hugo novel condemns the social injustices of 19th-century France? Begun in 1860, which major golf tournament is held each year in the United Kingdom? Begun in 1877, which is the oldest of tennis's four Grand Slam tournaments?