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What the Critics are Saying:

"This is a remarkable book; the polymath author expatiates on subjects as varied as architecture, theology, jurisprudence, the art of war, and, of course, biology, as well as happily imparting the juiciest bits of imperial gossip. Part III, Bacterium, begins with a detailed account of the nature of the plague, traces its terrible spread across ancient Europe, and provides visceral descriptions of the ravaged Constantinople, 5000 citizens dying every day. The end of the world, thanks to a flea."

Talha Burki in The Lancet

"This is a very engaging, lively, and entertaining text that presents the story of the plague almost as a mystery tour…an impressively wide-ranging book covering epidemiology, medical history, economics, agricultural history, evolution, and architecture. Rosen marshals information from history, zoology, genetics, complexity theory, meteorology, and evolutionary history to present a fascinating account of the interrelationships between fleas, rats, bacteria, climate, and food supply…worth reading for the lively accounts of battle scenes and the movement of armies; sympathetic descriptions of early Christian debates about the nature of God and Christ alongside critiques of intelligent design; discussions of the structure of marble; explanations of the effects of bacteria on a flea’s stomach and appetite, and, ultimately, the effect all this had on an empire.”

Helen Blackman in The Journal of the American Medical Association

“Like dominos falling, a series of events that began in the latter part of the 4th century triggered the separation of the eastern and western portions of the Roman Empire. The Huns invaded Europe from the east and forced the Goths to flee across the Danube River into Roman territory in 376. The battle of Adrianople in 378 destroyed two thirds of the eastern Roman army and caused a definitive split of the east from the west. By the beginning of the 6th century, Justinian became emperor of the Eastern Roman Empire, and by 540, North Africa and most of Italy were under his control. But a new invader, Yersinia pestis, came to Egypt, and then to Constantinople in 542, and on to Western Europe and the Persian Empire. For the next two centuries, waves of plague struck throughout the Mediterranean, Western Europe, and the Middle East. The old Roman Empire and the Persian Empire were depopulated. Plague changed everything, and as it did again in the 14th century, it changed the course of history.

Rosen’s knowledge of these events is remarkable. His explanations of the interaction of Y. pestis with the immune system and of bacterial pathogenesis provide insight into a killer that shaped history… Justinian’s Flea is a well-researched book that is also a pleasure to read, and I enthusiastically recommend it.”

Raymond J. Dattwyler, M.D. in The New England Journal of Medicine

"Don't charge William Rosen with lack of ambition. Instead of biography or the thin slice of the past that has become popular with history publishers, he presents us with no less than the foundations of the modern world, as built by a man and an insect. The result is largely successful and engaging. While the reader occasionally loses his bearings in an account that spans 10,000 miles, a dozen peoples, biology, architecture and the law, he is also amazed that Rosen packs it all into only 384 pages… [In] this widest of wide-ranging books, he leaves no cause unconsidered and eloquently connects a flea's bite 1,465 years ago with the world as it is today."

Jay Hancock in The Baltimore Sun

"...Rosen succeeds brilliantly. He writes what might be called champagne prose: it slips down quick and easy but carries a punch. He covers not just the centres but the extremities of knowledge: this book touches on gravity fields, early modern microscopes, late Roman cavalry tactics, and load patterns in the Hagia Sophia...He also covers the extremities of Eurasia, moving from monasteries in Dark Age Britain to civil war in China and brooding monotheists in the Arabian deserts - a geographic range that carries within it Justinianic ambitions. Sometimes, it is true, the trip resembles a driving holiday in Portugal - superb landscapes but almost no road signs - but the journey is always a fascinating one."

Simon Young in The Telegraph

"As a feat of scholarship alone this book is extraordinary, but what really impresses is the sense of ease its author manifests in whatever subject he enters. It's as if he'd been granted the freedom of Late Antiquity at birth. Furthermore, he allows himself space; when a subject requires explanation, and that in turn requires digression, he grants both. You never feel that he's indulging in scholarship for its own sake. I have to salute any author who can keep the reader enthralled by the intricacies of Byzantine architecture, let alone by protozoic metamorphosis -- and he does...Rosen's study comes very close to being a truly great work of history. His eloquence, wit, narrative skill, learning and (one dares to add) compassion, hoist this book above the miasma of its deeply sombre subject and make it, strangely, a joy."

Murrough O'Brien in The Independent

“This ambitious and learned book is destined to be a librarian's nightmare. How on earth to categorise it? Justinian's Flea is, among other things, a work of political, military, medical and cultural history. It may even have a reasonable claim to being a work of zoological history too...Mr Rosen argues his position methodically and thoughtfully. He has a lot of ground to cover and he will not be rushed. So there are chapters not only on Justinian and the plague but also on the migration of the Goths, Visigoths, Ostrogoths and Huns; on Byzantine architecture; on Roman law; on China and the silkworm; and on the emergence of Islam...All of this he deals with very well. Scholars may quibble with certain particulars but ordinary readers will be swept along by the strong current of Mr Rosen's good-natured erudition.”

The Economist

"In this eccentric and erudite book, in which a flea looms as large as an emperor, Rosen sets out to establish the forces that transformed the Mediterranean world of late antiquity into medieval Europe. Justinian's Flea is a massively ambitious work that covers a great deal of ground. It is a history of the eastern Roman empire and its many enemies, as well as a survey of the great city fo Constantinople, a new Rome straddling seven hills and smelling strongly of fermented fish sauce. This book also contains a detailed account of the evolution of the bubonic plague and how it weakened the empire's resistance to the conquering armies of Muhammad. It discusses how the Roman empire's collapse gave birth to the proto-nations within it, and how the rise of Islam helped to shape the identity of the European superstate of Christendom. [An] impressive study of the bubonic plague and its impact on history."

Ian Pindar in The Guardian

[Note to readers: I debated long and hard about including the following review, a highly negative one, from Peter Sarris, a Lecturer at Trinity College, Cambridge (whose work, by the way, is cited briefly, but positively, in Justinian's Flea).]

"It is not that, in its own terms, this is a bad book as such (although the structure is ill-disciplined and the prose, on occasion, over-written), nor that its subject matter is unimportant. The real problem is that it tells us almost nothing that we have not been told before, comparatively recently, and indeed by other books aimed at a general readership. There is only one significant idea in the entirety of its 367 pages that could be described as both original and interesting (it relates to China). The rest is either old hat, or has been worked up more effectively by other people… whether or not one regards [Rosen’s] conclusions as overblown is beside the point. The real problem is that pretty much exactly the same claims were made by the archaeologist and journalist David Keys in his 1999 book Catastrophe – An Investigation Into The Origins Of The Modern World …Keys’ book received widespread publicity and resulted in a spin-off television documentary that soon made its way onto cable (and in which, it must be admitted, this reviewer appeared). Indeed, on a number of occasions, Rosen himself refers to Keys’ work. Keys’ book has since been reprinted – so why do we need to be told the story again?… we have to ask, why write this book? The obvious answer is enthusiasm. Rosen is clearly fascinated by the world of the sixth century and wants to share what he has learned with others. But the enthusiasm of the author cannot of itself justify such egregious reiteration."

Peter Sarris in Scotland on Sunday

[Note to readers II: While I share some, though not all, of Mr. Keys' conclusions, his book is both wider and narrower than mine. Catastrophe argues that a climate change caused by a worldwide dust veil not only precipitated the Justinianic Plague, but civilization-hammering consequences from Korea to Mesoamerica, and as a result, spends more time in Japan and Mexico than Constantinople. It mentions neither Belisarius's campaigns nor the building of the Hagia Sophia -- a significant portion of the 367 pages of Justinian's Flea -- and Justinian himself appears on only three pages.

Mr. Sarris has informed me directly that the review above barely touches on his distaste for my book, which he calls dreadful. To him, and to anyone who shares his opinion, I can only apologize for not having written a better book.]

"A history of the Empire before Justinian took it over, [which] then runs confidently through to the last days that ended with the fall of Constantinople to the armies of Muhammad. Assertively modern in language and attitude, Rosen’s multi-disciplinary Byzantine history deals not only with fatal microbiology but also celebrates Justinian’s major achievements."

Iain Finlayson in The Times (London)

"Rosen] conveys the significance and excitement of Justinian’s achievements, from the building of Hagia Sophia to the codification of Roman law, without falling for all Procopius’s lurid gossip. He also does a good job in telling the scientific story of the plague... I found his account of how the plague organism developed, how it mutated and was transmitted to humans, and how we can still track its progress on the ground, a fascinating one."

Mary Beard in The Sunday Times

(though, to be fair, Professor Beard was unpersuaded by the book's argument about the historical importance of the plague, writing "I cannot help feeling that natural catastrophe is too slick an answer to be much use as a historical explanation on this scale.")

"Rosen relays eyewitness accounts of the Justinianic plague, with which he integrates the modern scientific understanding of Yersinia pestis and its carrier, the rat...Deeply steeped in the literature of late antiquity, Rosen wears his erudition lightly as he weaves interpretations into a fluid narrative of the era's geostrategic possibilities before the final onset of hte Dark Ages."


“Rosen absorbingly narrates the story of how the Byzantine Empire encountered the dangerous Y. pestis in A.D. 542 and suffered a bubonic plague pandemic foreshadowing its more famous successor eight centuries later… readers of Collapse and Guns, Germs, and Steel, Jared Diamond's grand narratives, will find this a welcome addendum.”

Publishers Weekly

“A polymathic account of the rise and reign of the Emperor Justinian (a.d. 527-565), whose greatest nemesis turned out to be a microscopic terror he could neither see nor identify… Rigorous, highly informative history written with passion, panache and an appealing bit of attitude.”

Kirkus Reviews (starred)

“William Rosen doesn’t just give us the most believable, the most human and the most fully rounded Justinian ever. He also conjures up a vivid picture of the age, in a compelling style that makes his weighty learning light.”

- Felipe Fernández-Armesto, author of Millennium and Civilizations

"An engrossing and insightful account of one of the most important but little known medical disasters in human history."

- John Kelly, author of The Great Mortality: An Intimate History of the Black Death, the Most Devastating Plague of All Time

“What a richly-detailed and thought-provoking book! I got stuck into William Rosen's fascinating chronicle with all the appetite of a flea settling on the brawny arm of one of Justinian's cataphracts.”

- Robert Lacey, author of The Kingdom

“We live at a time when the Pope’s quotation of a Byzantine emperor can cause an international incident. William Rosen’s fascinating new book offers a timely portrait of the greatest Byzantine emperor of them all – and explains, in compelling detail, how the golden age of Constantinople was blotted out by a catastrophe as momentous as any in history.”

- Tom Holland, author of Rubicon: The Triumph and Tragedy of the Roman Republic, and Persian Fire: The First World Empire

Justinian’s Flea is narrative history writing at its best. Breathtaking in its scope, the book presents a confident mix of history, science, architecture, theology, military strategy, law, engineering and medicine to tell the story of how plague transformed the classical world and gave birth to mediaeval Europe. William Rosen’s canvas stretches from China to Spain, and Britain to Arabia, and his intriguing cast of characters includes emperors, priests, soldiers, and engineers as well as rats, fleas and silkworms. Justinian’s Flea transforms our understanding of many key events in the history of the last two thousand years, from the decline of Rome to the rise of Islam and beyond.”

- Karl Sabbagh, author of A Rum Affair and Palestine: A Personal History

“Ambitious and exciting, witty and elegant, this is a big book in every sense, and packed with big ideas. William Rosen takes one of history’s great cause-and-effect problems and turns it into a work that is entertaining and illuminating in equal measure. Along the way he comes up with interpretations of a little-understood era that delight and sometimes dazzle. From the theological puzzles of Gnosticism, neo-Platonism and the Arian heresy through the pathology of a flea-bite to the appropriate use of heavy cavalry, the complicated and the convoluted become comprehensible...and fun.”
- Phil Craig, co-author of Finest Hour: The Battle of Britain