In the early sixteenth century, a young English sugar trader spent a night at what is now the port of Agadir in Morocco, watching from the tenuous safety of the Portuguese fort as the local tribesmen attacked the "Moors." Having recently departed the familiar environs of London and the Essex marshes, this was to be the first of several encounters Roger Barlow was to have with unfamiliar worlds.

Barlow's family was linked to networks where the exchange of goods and ideas merged, and his contacts in Seville brought him into contact with the navigator, Sebastian Cabot. Merchants and...