Kirkus Best Book of 2025 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 groundbreaking new knowledge of weather patterns and ocean currents, Portuguese mariners set the tone for the Age of Exploration. But their navigational achievements had horrific consequences for the people of western Africa: subjection to the slave trade. Patricia Seed examines the historical and climatic odds that Portuguese seafarers overcame to be the first Europeans to tame the Atlantic. Using insights from fields ranging from oceanography to ethnography, she recounts how the Portuguese rapidly innovated and achieved profound new understandings of the ocean and sailing. At the same time, she foregrounds the reality that these innovations enabled them to inflict unimaginable cruelty as, against sometimes violent resistance, they forged what became their spoils of empire: the lucrative trade in human cargo that enslaved millions across Africa and beyond. Sails and Shadows is a history of incredible ingenuity outweighed and overshadowed by the horrors it wrought.