European sailors first happened upon Easter Island - a tiny island in the South Pacific Ocean - on Easter Sunday, 1722. Yet archaeological explorers didn't arrive until 1886. A U.S. crew led by William J. Thomson investigated Easter Island's stone heads, called moai, and uncovered many mysteries: Who built them and when? What was their purpose? How did Easter Islanders raise the massive stones? Later researchers found some answers. In 1914 British...