The compass opened up the world to exploration and discovery. The first compasses comprised a magnetic needle floating in a bowl of water, with the needle suspended on a thread or threaded through a reed. This principle was already known to the Chinese in the 3rd century BC and was first used by feng shui priests to tell them where and how to build. It was adapted to maritime navigation by Chinese sailors around the year 1000. The Arabs perfected this by mounting the needle on a pivot. The compass arrived in Europe between the 10th and 11th centuries, enabling sailers to cross the oceans and explorers to discover the continents.