Charles had adopted the motto “Plus ultra” to emphasise his imperial power, so underneath the restrained eagle, the defenders of Metz wrote “Non plus Metas”, meaning both “not beyond Metz” and “not beyond the boundaries”.

For an entire millennium, from 800 to 1806, from its birth with Charlemagne to its death at the hands of Napoleon, the Holy Roman Empire’s borders defined the heart of Europe. As the dust jacket for Peter Wilson’s new book puts it, Europe made “no sense without it”. Centred on Germany, it also encompassed much of what is now France, Austria, the Netherlands, Belgium, Switzerland, the Czech Republic, Poland, Slovenia and Italy.

Yet for over two centuries, the empire has had a bad reputation. Voltaire disparaged it as not holy, not Roman, and not an empire. James Madison deemed its institutions “feeble”, its history one of “general imbecility, confusion, and misery”. And Leopold von Ranke, father of the modern study of history, thought it one long decline and failure. With exhaustive detail, Wilson argues that these titanic figures were wrong. He encourages us to reassess the history of Europe with an empire state of mind.

Wilson makes the complex understandable, but the sheer depth and daunting length of the book – and its focus on ideas and institutions rather than individuals and stories – may mean that only the most motivated non-academic readers are likely to reach the end. For those who do, there are many interesting and provocative ideas.

A patchwork of principalities, free cities, archbishoprics, confederations, grand duchies and even full kingdoms, the imperial system worked surprisingly well. Neither a “single command chain nor a neat pyramid”, it was instead a framework, focused on consensus not coercion, accepting rather than rationalising anomalies and diversity. Its guiding principle was “workable compromise” (in practice, often fudge) but it was not impotent: pioneering the first commercial postal service is one of many examples of the empire’s highly developed governance.

This decentralised structure was supported and reinforced by a multicentred society. Unlike the national dominations of London and Paris, the empire had many different concentrations of power, business and culture: Vienna, Prague, Antwerp, Hamburg, Augsburg, Milan. Power was “local and particular”, not universal or linear. Ordered imperial society encompassed diverse peoples and corporate groups, and the empire’s role was to protect their patterns and hierarchies. It survived centuries of change, the schism of the Reformation, and even the catastrophe of the thirty years’ war.

As one of its last chancellors commented, while it “might not conform to all the building regulations”, it was a “permanent Gothic structure … in which one lives securely”.

Instead of criticising it for the lack of a centralised state, Wilson’s focus is how the empire’s territories and groups generally succeeded on their own terms. While there were many failures of consensus – endless tolls restricting trade; dozens of shifting currencies; outdated fiscal structures – it is only in hindsight or ideology that the 18th-century empire appears as dying. While not overlooking the destabilising effect of Prussian and Austrian expansion, Wilson shows that the growth of territorial states was integrated within the imperial framework, rather than destroying it from the inside out. Had Napoleon not intervened, the empire could have persisted well into the 1800s until it felt the “levelling and homogenising forces” of industrialisation.

The empire has often flummoxed scholars because its history is so difficult to tell. After 24 volumes explaining the imperial constitution the 18th-century legal scholar Johann Jakob Moser effectively gave up, concluding that “Germany is governed in the German way”. A comprehensive narrative of the empire’s millennium would consume a small forest – Joachim Whaley ’s excellent recent history of its last 300 years required two volumes – and be dizzyingly complicated.

To escape such pitfalls, Wilson takes an approach somewhat reminiscent of Marc Bloch’s 1939 classic Feudal Society , assessing the institution in its entirety (“like an eagle flying over the empire”). Rather than telling a chronological story, Wilson asks what it was, “how it worked, why it mattered” and inquires into its legacy for today. The book is structured in four parts: ideal, belonging, governance and society. It is a challenging format, but it allows conceptual analysis that would be impossible in a linear narrative.

Wilson aims to avoid the pervasive idea of history as a road to modernity, a tradition that often relegates the empire to the slow lane while England races ahead. Indeed he argues that “the empire’s greatest posthumous influence lay in how criticism of its structures created the discipline of modern history”: ideas of progress and national histories have coloured our view of it ever since. The empire did not “fail” to build a centralised German state or nation because “no one felt either needed building”.

Rather than a distant irrelevance, the empire was an important focus of attachment for its people. Individuals and groups had multiple identities within an imperial framework of solidarities and hierarchies. A Berliner could be a Lutheran, a city burgher, a father, a guildsman, and a Prussian. Many weaker groups, such as religious minorities and those with grievances against their rulers, saw the empire as protection from the strong. Far from it being just “German”, Wilson emphasises the overlooked engagement of Czechs, Italians and others in the imperial framework, all the way through to its end.

Not many books stretch from Charlemagne to Ukip, but today’s multinational European framework is central to Wilson’s epilogue on the empire’s afterlife. The EU shares many of the its structures – permeable boundaries, multilayered jurisdictions – and its problems: Byzantine complexity, a reliance on fudge. Yet while Eurofederalists and Eurosceptics both see political institutions as centralising rulers of hermetically sealed areas, the empire reminds us that that was not Europe’s past, and – with disenchantment in our current model of democracy – is unlikely to be its future.

Wilson argues that legitimacy can come from debate, not just votes; citizenship from civil society, not just formal rights; and that politics can be a multicentred process of consensus bargaining. He is too good a historian to suggest that the empire – with its stark pre-modern hierarchies and inequalities – is a blueprint for today. But he is right to suggest that it could help us understand current problems more clearly.

The Guardian