Surveying the various models available in 1787 for governing the still-constitution-less United States, James Madison, perhaps the shrewdest of the Founding Fathers, was certain of one thing: the Holy Roman Empire, at that date the largest of all European states, exemplified the one type of federal constitution that he most wanted to avoid. The Empire was a body, he concluded, ‘incapable of regulating its own members; insecure against external dangers’, and with a history marked by ‘general imbecility, confusion and misery’. It is no coincidence that the Holy Roman Empire has acquired a new and topical prominence in Eurosceptic punditry as a mirror for the ills of the European Union. Like the Holy Roman Empire of old, the EU is hard put to regulate its own members, incapable of securing its internal or external borders, and beset with consensus-obsessed processes of decision-making that render decisive collective action all but impossible. The lessons of history are clear, it is claimed: supranational federalism has been tried before – and it doesn’t work.

Such glib conclusions are, of course, at best half-truths. Whatever their validity as a critique of the EU, they do serious injustice to the Holy Roman Empire. As Peter Wilson’s huge – and hugely impressive – new study makes clear, these comparisons arise from an astonishingly widespread ignorance of what