Found within the subtropical high-pressure belts, the Horse Latitudes are areas where the Hadley Cell air descends. This descending air is compressed and warmed, which inhibits cloud formation and results in clear skies and minimal rainfall. Because the air is moving vertically downward rather than horizontally, surface winds are notoriously weak or non-existent. These regions are home to many of the world’s great deserts, such as the Sahara. For early mariners, these calm waters were a major obstacle, as the lack of wind could stall a voyage long enough to deplete water and food supplies for livestock.