The Zen brothers had nothing to do with Buddhism. They came from a well-heeled family in 14th-century Venice, where their palazzo still stands. What is less clear is whether they made the path-breaking early travels for which they are sometimes hailed. In his new book, Andrea di Robilant tells of investigating the brothers’ claim to geographical greatness by studying a volume, originally published in 1558 by one of their descendents, from the rare book room of the Biblioteca Marciana. The book included a map that pointed the way to the island of Frisland, somewhere beyond Scotland. So tantalizing was Frisland, di Robilant writes, that the map caused the British Crown to send “Martin Frobisher on a fruitless journey to discover [the island] and claim it for England.” Di Robilant acknowledges that “today the vast majority of geographers and historians generally assume the [travel] story is apocryphal, especially in northern European countries, where the mere mention of the Zen brothers can still provoke an irritated twitching of the brow.” But in making his own journeys in the Zens’ alleged footsteps, di Robilant learned many things, including how the early inhabitants of Iceland practiced Christianity. Priests commonly kept concubines and sired children, and instead of using cold water for baptism as the Church advised, Icelanders preferred “to take the sacrament while bathing in the hot springs near their homes.”