In 1492 Columbus sailed the ocean blue. The oft-repeated rhyme memorialises the moment that the Atlantic, and what lay beyond, entered the realms of Western historiography. A more expansive view of the history of the world’s second-largest stretch of sea accommodates the intrepid Viking voyagers who used the Faroe Islands, Iceland and Greenland as gigantic stepping stones to North America almost five hundred years before Columbus crossed the Atlantic. John Haywood’s Ocean turns the conventional narrative on its head, making the Genoese navigator’s voyage not the beginning of the story, but the culmination of millennia of ventures into the unknown.

Haywood takes us deep into prehistory, starting with the first primates to cross the Atlantic – not Vikings, but monkeys travelling on precarious rafts made of natural vegetation some thirty-five million years ago. The first human interest in the ocean is suggested by mounds of mussels and limpet shells in a cave north of Cape Town, dating from 164,000 years ago. A taste for shellfish must surely have led humans to wonder at what exactly lay beyond the blue horizon.

Trade was the first driver of exploration and Haywood paints a fascinating picture of the growing commercial networks that knitted the eastern Atlantic world together. The Bronze Age fortified castros of Portugal – such as Zambujal, whose elite had access to Baltic amber, North African elephant ivory and ostrich eggs