How the early Portuguese Empire facilitated the modern slave trade. The Portuguese conquered the challenges of sailing the unforgiving Atlantic Ocean, extending their colonial empire along Africa's western shores. With their dedication to developing new sailing techniques and a groundbreaking new understanding of weather patterns and ocean currents, the Portuguese set the tone for the Age of Exploration. But their navigational achievements had horrific consequences for the people of western Africa: subjugation to the slave trade.   Patricia Seed examines the historical and climatic odds that Portuguese seafarers had to overcome to be the first Europeans to tame the Atlantic. Using scientific tools from fields ranging from oceanography to ethnography, she recounts how the Portuguese rapidly innovated and developed profound new understandings of the ocean and sailing. At the same time, she foregrounds the reality that these same innovations enabled them to inflict unimaginable cruelty as, against sometimes violent resistance, they forged what became their spoils of empire: the historic trade in human cargo that enslaved millions across Africa and beyond. Sails and Shadows is a history of incredible innovation outweighed and overshadowed by the horrors it wrought.