What has Byzantium to do with the Ottomans? It was indeed Mehmed II who entered Constantinople on May 29 1453 and put an end to more than 1,100 years of Byzantine rule. But he was not even the first: the armies of the Fourth Crusade had taken and sacked the city in 1204 and set up a Latin Empire which lasted until Constantinople returned to Byzantine hands in 1261. More recently, it had been under siege from Bayezid I for eight years from 1394 to 1402, and had come near to being taken by the Avars in 626 and the Arabs in 717-18.

But Mehmed II was determined. The Byzantines, pitiably few in number, were trapped by the twin Ottoman fortresses that faced each other across the Bosphorus. They knew that it was only a matter of time before the city was taken, and their pleas for help from the West met with little success; despite the legitimate hopes of those who had supported religious union with Rome, what little help they did obtain came sadly too late. Once victory was assured, Mehmed rode his horse to Haghia Sophia and entered the church in the symbolic gesture of a new ruler taking possession of a fallen empire. Constantine XI Palaeologus, the last Byzantine emperor, perished in the last of the fighting, though in the historical imagination of the survivors he lived on and there were those who claimed descent from his line even in the present century.

The fall of the city was a catastrophic event for Christians, and especially for Greeks. It was and still is commemorated in songs and laments, and recorded by Byzantines, westerners and Turks alike. Though few Greeks remain in Istanbul today, and the traditional splendour of the Oecumenical Patriarchate in Phanar belies the precariousness of its existence there, the Byzantine and Orthodox past is kept very much alive. Reports that Haghia Sophia might again become a mosque are more than enough to revive painful memories.

Yet Palaeologan Byzantium could hardly be called an empire. Reduced to a minuscule amount of territory round the city, it was not very different from the other Byzantine principalities which came into being after the Latin conquests - Mistra, Morea, Nicaea, Trebizond. Families claiming descent or kinship with the imperial line in Constantinople established themselves as rulers, and the impressive buildings of the period, especially the churches, testify to the patronage and wealth of individuals. One such was Theodore Metochites, the patron and restorer of one of the finest monuments of the period in Constantinople, the Kariye Djami, formerly the monastery of Christ in Chora, with its gloriously expressionist frescoes and mosaics. The Byzantines of this period built in brick, but in a monumental and self-confident style.

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Self-confident, too, was the Emperor John Cantacuzene (1347-54), who is the subject of Donald Nicol's book. He wrote a history of his own time, and was bold enough to abdicate the throne and choose to spend the last 30 years of his life as a monk. By this time Byzantium was surrounded by powers as powerful or more powerful than itself, and with these - Serbia, and the Osmanli Turks under Orhan - John tried to deal. It was not his own fault that he also met with natural disasters like the Black Death or the earthquake which struck Gallipoli in 1354. Religious and political history went together in these years; members of the imperial and aristocratic families endowed fortress-like monasteries which they themselves and their descendants would then enter, and contentious religious issues were as important in contemporary politics as military and diplomatic considerations.

John Julius Norwich's chapter on John Cantacuzene has the same title, "The reluctant emperor", as Nicol's book. Lord Norwich's very readable Byzantium, The Decline and Fall concludes a trilogy on the history of Byzantium. Taking its cue from the approaching end of the city, its tone is fatalistic; the Byzantines, he says, do not deserve "the obscurity to which for centuries we have condemned them", but he nevertheless sees them as already doomed, their fate symbolised in the broken and battered Long Walls that "stand as the city's grandest and most tragic monument".

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It is a view of Byzantium which has impeccable credentials, and one rendered all but irresistible by the stirring story of the fall of Constantinople. Whether seen in contrast with classical antiquity, or in conjunction with "the sick man of Europe", Byzantium evokes notions of decline and rigidity. Though not possessing the fascinations of the Turkish harem, as recorded in The Sultan's Seraglio by Ottaviano Bon (the 17th-century Venetian representative at the court of Sultan Ahmet I) here attractively edited by Godfrey Goodwin, Byzantium has nevertheless appeared to share in the harem's feminine, and therefore corrupting allure.

In contrast, scholars such as Rosemary Morris and Michael Angold represent a newer and more realistic view of Byzantium as a resilient medieval society which experienced substantial change and development during its long history. This Byzantium survived the massive Arab conquests of the 17th century, reorientated itself away from the classical Mediterranean and towards the north and transformed its military, administrative and tax base to the extent that by the tenth century it had developed an extensive network of diplomatic contacts and was able to win back territory lost to the Arabs in Asia Minor or the Slavs in Greece.

Many of the details of this transformation, which happened at a period for the most part earlier than that treated by either of these scholars, must remain extremely obscure. For shedding light on the economic recovery, however, we can thank some younger British scholars like Alan Harvey and Archie Dunn, both products of the Byzantine centre at the University of Birmingham. Rosemary Morris has now used the recently published charters of the monasteries on Mount Athos to demonstrate in Monks and Laymen in Byzantium the economic interdependence of church, monastery and society in the middle Byzantine period, from the end of iconoclasm in the ninth century to the end of the reign of Alexios I in 1118.

From the ninth century onwards, historical evidence begins to become more plentiful, under the twin influences of a revival of literature and learning and of the release afforded by the settlement of the religious and political divisions which had dominated the period of iconoclasm. Not only do we know more from literary and artistic sources and liturgical and other compilations about the monastic houses and foundations of the following centuries, the Athonite charters now published by French scholars, and used by Morris, begin to reveal the important economic role played by the monasteries as owners of land and overlords of dependent peasantry.

Monastic involvement in trading activities developed to such a level that emperors such as Constantine Monomachos in the 11th century might be called on to intervene to end disputes between rivals. Imperial tax exemptions allowed some monasteries to become powerful and rich enough for reforms to be felt necessary with the aim of recovering centralised imperial authority. Nevertheless, imperial and aristocratic patronage of monasteries continued in the Comnenian period, as Angold emphasises.

The 11th and 12th centuries represented a period of great importance for Byzantium. Constantinople, which had shrunk since the Arab conquests from a city of perhaps half a million to less than a quarter of that size, was once more a great city; Geoffrey of Villehardouin estimated its population at 400,000 in 1204. The imperial traditions continued; the Comnenian emperors practised patronage, observed the rituals of the court, and when necessary engaged in war and diplomacy, but a group of powerful families constituted the elite, and kinship became an important element in imperial policy and control.

It was a period of intense literary activity, which saw an outpouring of literary works in high rhetorical style as well as the beginnings of Greek vernacular literature. In place of the ideal of celibacy extolled in earlier ascetic literature, marital love and fidelity were celebrated in aristocratic writing, and dynastic marriages were the order of the day.

Yet there were deep divisions, providing many opportunities for satire and criticism. Public heresy trials were accompanied by sharp written attacks on the traditional targets - Jews, Muslims, Monophysites and Bogomils - as well as the beliefs and practices of the Latins. The years before 1204 were tense, with an uprising in 1185 against the Emperor Andronikos, who had himself come to power after a coup in 1182, and the overthrow of his successor Isaac Angelus by the latter's brother only ten years later.

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Against much modern interpretation, Angold accepts the contemporary view which attributed these developments to political and moral malaise. Not even the church could give a lead, for it too, he says, was paralysed by internal bickerings. When the sack came, it was disastrous. The Latins expelled the Byzantine government and removed from Constantinople to the West dozens of its most precious classical statues and holy relics.

But the long history of Byzantium was not over in 1204. Indeed, resilience is among the foremost qualities demonstrated by the Byzantine state. In the later 11th century it suffered one of its most devastating defeats, at Manzikert in Armenia at the hands of the Seljuks, after which there was a severe decline of Greek and Christian influence in the traditional heartland of Anatolia and its eastern borders.

The same period saw the impact of the crusades, which was to have equally destructive consequences for Byzantium. Yet contacts with the West were far from being all negative. Byzantium shared what seems to have been a general population growth, and took advantage of trading opportunities with the Italian cities. Western influences are detectable in writing and social customs, and even the conquest of 1204 was to leave an architectural legacy of Frankish castles and Latin styles of church building.

Byzantium's cultural contacts with the West, especially Italy, steadily increased, and in turn Byzantines established themselves in Venice and other centres in considerable numbers after the fall of Constantinople. Byzantine culture had also flourished in centres outside Constantinople during the last centuries of the empire; Mistra, with the Platonic Hellenism of Gemistos Plethon, and Thessaloniki, the home of Gregory Palamas, the opponent of western theological influence, between his stays on Mount Athos, could make as good a claim as the intellectuals of the capital to be the guardians of Byzantine tradition.

State formation and state survival depend on armies and resources. This is especially so in the cases of Rome and Byzantium, where the ability to support an army large enough to defend, or indeed expand, the state represented the biggest item of state expenditure and its major organisational problem. The capacity of these empires to raise sufficient taxes to support this expenditure, when most production still came from the land, and there was little if any technological development, is one of their most remarkable features.

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Naturally enough there were major changes over so long a period. Warren Treadgold begs the question in writing of the "Byzantine" army over the period starting with the accession of Diocletian in AD 284; most historians would see the army of that period as essentially late Roman, even though there is disagreement as to how long it lasted in the form established under Diocletian and Constantine, and indeed on how large the establishment actually was. It is possible, although some historians including Treadgold have recently argued against it, that after the vaunted "reconquest" of the west under Justinian, the army became seriously depleted. In the seventh century, the Arab conquests deprived Byzantium of much of its land, and one archaeological survey after another demonstrates a dramatic drop in coins, artefacts and indications of habitation. How the state (now undeniably "Byzantine") managed to reconstitute itself, its tax base and its army in these circumstances remains extremely obscure.

However confident Treadgold's account may seem, with its detailed tables of statistics on pay and military strength, other historians see this period as marked by ruralisation and decentralisation, with the emergence of regional "themes" with their own armies under the control of local generals. The implications of this for the continuation of the traditional late Roman army system must have been serious. If the Byzantine army in the early 11th century, when Basil II reduced Bulgaria to the state of a Byzantine province, was more recognisably the army of a powerful state, this was surely connected with the economic growth and population rise which can be detected meanwhile. But few empires can sustain themselves uninterruptedly over a matter of centuries, and even the Bulgarian victory was followed less than 50 years later by crushing defeat at Manzikert. Writing about the history of Byzantium is not an easy matter. But books that look too confident in their assertions, or even books which present an over-detailed narrative, are in general to be used with caution.

One of the most important types of evidence for understanding Byzantium comes from art history. Not only is Byzantine art undoubtedly a major source of the appeal of Byzantium in modern times, but the rich surviving material is a fundamental resource for historians and art historians alike. Doula Mouriki, one of the principal editors of Byzantine East, Latin West, sadly died while the book was in preparation. This splendid volume honours the memory of Kurt Weitzmann, one of the most influential of Byzantine art historians in this century. Weitzmann was much concerned with stylistic and historical change, including the transition from classical to Byzantine, and with the sources of Byzantine iconography, especially in the field of manuscript illumination.

A group of some 70 leading scholars have contributed articles in several languages in his honour, in many cases reflecting Weitzmann's particular interests. Together they give a very comprehensive introduction to the range of issues and the material available in the vast field of Byzantine art, although one should not expect to find in a volume in honour of Weitzmann, many examples of the more theoretical, functional or poststructuralist analyses which are typical of others working in the field, or indeed the strong emphasis laid by some on Byzantine art as part of material culture rather than as a matter of iconography and style. Inevitably also the contributions vary; this is a volume of homage by pupils and colleagues who are themselves for the most part significant scholars in their own right.

It is tempting to identify Byzantine art as religious art, though some of the contributors to the Weitzmann volume have themselves drawn attention in their work to the secular arts in Byzantium. Nevertheless, orthodoxy is a distinguishing feature of Byzantine culture, and a high proportion of Byzantine art was concerned with religious subjects. It is the supposed spirituality and the "eastern" quality of Byzantine icons that draws the observer, and whose essence Weitzmann himself sought to capture in his writing. It is therefore not very surprising if some Byzantinists are at pains to dispel these associations, which seem to embody the very features of Byzantium which lead to its too-ready assimilation with the Ottoman empire and to a degree of Orientalism in the way in which it has been interpreted. The fact that the conquering Ottomans were Muslim and the Byzantines Christian is deeply embedded in the historiography and interpretation of the two societies; indeed, its repercussions are still with us.

In one sense Byzantines and Ottomans are elided into an "eastern" model of interpretation already present in Gibbon's Decline and Fall. But Byzantinists themselves have generally drawn a sharp line at 1453, and if they were interested at all, adopted the negative attitude towards the Ottoman empire that is exemplified in Steven Runciman's classic study The Great Church in Captivity (1968), whose very title evokes what the author calls "the dark centuries" between 1453 and the Greek war of independence. There is a substantial amount of surviving Ottoman documentary material relevant to the later history of Byzantium, and this has been exploited by some Byzantinists, such as Anthony Bryer, but the fact that, in general, the Ottoman period has been even less studied in this country than Byzantium is itself both a product of and a contributor to the general view. There is also a cultural difficulty: while Greeks and Hellenophiles are keen to remind us of their past, even if that past is sometimes presented in elegiac tones, the voices of modern Turkish scholarship do not as a rule make themselves heard as a counterbalance.

Philip Mansel's attractive book Constantinople, City of the World's Desire, reminds us of difference. It starts with the efforts of Mehmed after the conquest of the city to recreate it as an Ottoman capital, and ends with the exile of the last Caliph with his family in 1924. After the reforms of Mustafa Kemal, commonly known as Ataturk, Greek, Armenian and Jewish businesses were taxed out of existence, while thousands of Greek Christians who had been forced to leave what had once been the territory of Byzantium in the exchange of populations returned to a Greece that had never been their home. Ankara, not Constantinople, was to be the capital of the new Turkey.

Mansel's account of the final phase of Ottoman Constantinople, when the city was occupied for almost five years by the Allies, is among the most fascinating parts of his book. There are many other details for readers to enjoy, for instance, his account of how in 1856, as the Crimean War neared its end, the sultan attended a ball at the British embassy, with the embassy staff in 18th-century costumes; a few months later he reciprocated with a splendid banquet at the new Dolmabahce palace, and church bells rang for the first time in the city since 1453.

Mansel also writes well of the display which characterised Constantinople during the reign of Suleyman the Magnificent, for example the circumcision ceremony of his three sons in 1530. He draws a contrast between the sultan and the Byzantine emperor; both, however, ruled amid splendour and court ritual, and made regular progresses through the city or further afield. The people of Constantinople, he writes, with their love of pomp and splendour, were "instinctive imperialists".

In contrast, while Suleyman the Magnificent and his Age was inspired in the first place by the very successful exhibition under that title at the British Museum in 1988, this collection of essays and those included in Imperial Legacy seek to go beyond the "dominant barrier of Otherness" in Ottoman studies and offer an analysis of Ottoman power and of the ideology of statecraft, or, in the case of the important essays in Imperial Legacy, of the impact of centuries of Ottoman rule on the Balkans and Middle East. The latter in particular is urgently needed if we are to begin to understand our present problems in those areas, but it cannot be studied in separation from the former.

L. Carl Brown of Princeton University has drawn together some of the most distinguished scholars in the field from NorthAmerica and Europe to investigate the various ways in which a history of Ottoman rule in the past still influences state formation and cultural practice in the modern world, in countries as different and as far apart as Bosnia, the Middle East and Algeria. Its illustrations underline the argument of the text: they include 19th-century cartoons from Punch and elsewhere, showing the mutual misunderstanding between the Ottoman empire and Europe, and a photograph of the 16th-century bridge over the Neretva river in Herzegovina, destroyed by Croat fire in 1993. This is an important and scholarly book which nevertheless provides an excellent introduction to the historical dimension of some crucial contemporary issues.

What then can be learned from considering Byzantium and the Ottoman empire together? One benefit is that Byzantium is thereby released from the crippling burden of adverse comparison with classical antiquity, though this has to be set against the danger of Orientalism that I have already mentioned. A greater benefit is the opportunity it provides of comparing imperial structures (as in Brown's introduction to Imperial Legacy), especially in relation to the treatment of minorities and the role of religion. Pluralism and tolerance were in both empires the norm, but might always be replaced by temporary phases of repression. The relation between the ruler and his rivals and the composition of aristocracy are also topics which can be usefully compared.

Both empires proved themselves highly adaptable, and both changed many times during their existence, in response to external or internal pressures, or to geographical differences. How they managed to survive as empires despite changes in the ruling dynasty is an issue which needs investigation. In these and other ways, their mechanisms of empire are still to be studied in the amount of detail which has been devoted to the Roman empire. Yet they would tell us a great deal about the present-day Balkan situation, and might save us from some of the hasty and superficial judgements made in the west on the fall of Communism.

Both of these were empires that have fallen. It is far too easy, however, to appeal to "decline", corruption or the moral decay of a system as an explanation. Neither Byzantium nor the Ottoman empire were empires with a single unchanging character for the whole of their existence, and both proved remarkably resilient and tenacious, not least in their later legacy. That is a thought to keep in mind for our own times.

Averil Cameron is warden, Keble College, Oxford, and was formerly professor of Late Antique and Byzantine studies, King's College London.

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