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 archaeologists Scoresby and Katherine Routledge discovered clues to how past islanders had carved the statues. In 1955 a team led by Norwegian explorer Thor Heyerdahl unearthed new ideas about the role the stone heads once played in the island's religion, as well as how people had placed the statues on the island's shores. Work and study on Easter Island have continued, but questions about the island's past and the massive moai remain. Why did islanders stop making moai? Will researchers ever know how people raised the huge heads? These mysteries are still unsolved.