The fourth volume in David Weber’s Safehold series continues the three main themes of the previous novels: the conflict between faith that goes against reason and faith in harmony with reason; the historic role of the Anglosphere in nurturing freedom; and the tactics, technology, and logistics of naval warfare. The center of the conflict, the island nation of Charis, an analog of England on a planet several light years distant that shelters the last remnants of humanity, has undergone a religious schism with the dominant Church of God Awaiting, comparable to England’s break with Catholicism under Henry VIII, but for nobler motives. Now it’s embroiled in a struggle for survival and freedom, in the course of which it has variously allied with and conquered other island nations: Emerald, an analog of Ireland, Chisholm, an analog of France, and Corisande, possibly an analog of the United States. One of the Corisandian agitators against Charisan rule is a silversmith named Paitryk Hainree, one of Weber’s less subtle allusions to real earth history...and arguably a dubious analogy, in that it puts Safehold’s rebel against “England” on the side of submission to religious absolutism.

Even so, the narrative in this volume shows greater intensity than in previous volumes. The sea battles, in particular, are exciting and suspenseful, partly because Weber makes a point of showing them through the eyes of captains on both sides of each battle, and of giving both sets of captains virtues worthy of respect. In some measure, the Safehold books read like a panegyric to the British navy—and reflecting this, the naval warfare more nearly resembles that of the sixteenth century than that of the Tudor monarchy. But even though the other side is technologically outclassed at sea, Weber gives it its own assets: clever and determined captains and admirals, and a vast pool of wealth to support it, drained from the Church’s subjects through taxes and tithes.

A Mighty Fortress further develops the theme of the Church as a totalitarian organization, one willing not merely to crush dissenters but to torture and murder their families as well. But, like revolutionary France, it has the strength of being willing to tax and conscript the people it rules. On the other hand, the policies of its own fanatics are starting to drive away the loyalty of even some of its bishops. Even one member of the Group of Four has begun to maneuver toward more restrained policies, pointing toward the possibility of a reform or a further schism.

The title is obviously a reference to the famous hymn. But in the context of Safehold, it has other meanings. First, it refers to the traditional Charisian saying that the island is fortified with wooden walls—the hulls of its fleet. Second, it refers to the will of its people to fight and resist. And third, as King Cayleb’s mentor Merlin Athrawes tells him, it refers to the sense of duty of Charis’s people to defend each other, their faith, and their freedom.

In A Mighty Fortress, Weber has given us a new installment of a well-told adventure story, and one focused on the defense of values that libertarians care about: technological progress and individual freedom of choice.