In his book Stefan Burkhardt has set himself a formidable task. The stated intention of his work is to provide a comparative study of both the concepts and realities of empire (Kaisertum) in the medieval period (until the middle of the thirteenth century), and also into the nature of what he calls imperiale Ordnungen (a term which may be translated as "imperial constellations") in the Mediterranean, with a specific focus on the political entity commonly known in modern historiography as the Latin Empire of Constantinople (1204-1261). To tackle these research questions he has divided his work into three parts: concepts of empire (21-216), imperial constellations (217-256), and a final part on the relationship between empire and imperial constellations (257-370).
In the first part Burkhardt aims to define the essence of imperial rule compared with royal, princely, urban, communal or other types of medieval rule. In order to do so he analyzes these various forms of rulership, with a clear focus on imperial rule and especially on the Holy Roman Empire, the Byzantine Empire and the so-called Latin Empire as the prime examples of this latter category. Various features (representative culture, relationship to ecclesiastical authority, capital cities, Roman legacy, universalism, sacrality, the conflict between imperial aspirations and political realities, etc.) pass in revue, mostly on the basis of both older and recent historiography, with relatively little original exploitation of the medieval sources. While this is quite competently done with regard to the Holy Roman Empire, at the same time few new insights are to be gained.
Also, there is conspicuous disparity between the attention devoted to the Holy Roman Empire on the one hand, and to the Byzantine and Latin Empires on the other. The Byzantine casus is often treated rather succinctly (see for example his analysis of imperial salvatory functions (88-97), false emperors (113-117), coronation rituals (131-140)), while Burkhardt's analysis of the Latin Empire's casus generally lacks accuracy and depth. For example his treatment of the relationship between the Latin emperors and the papacy (54, 71, 88-97), of the supposed lack of awareness of the universalist and Roman character of the Byzantine Empire at the Latin imperial court (66-87), of the lack of recognition of the Latin emperors' imperial rank in the West (117-138), of the imperial title and courtly titles (195-205) show a frankly alarming unfamiliarity with essential literature and sources. We will return to this when discussing the third part of the study at hand.
In his provisional conclusions at the end of Part I Burkhardt arrives at two main insights: essentially the empires under consideration can be typified as both virtual and hybrid in nature. While this is undoubtedly true, the déjà-vu-factor of such an observation is obvious. Any political construction with explicit universalist ambitions is of course doomed to not being able to live up the stated ideal, while the mutual influences between the Byzantine and Holy Roman Empires, and also the mix of both Byzantine and Western elements in Latin imperial Constantinople, have already been dealt with extensively by numerous scholars (to name but a few older authors: Jean Longnon, Antonio Carile, Benjamin Hendrickx, David Jacoby).
In the second part of his work Burkhardt introduces the concept of Mediterranean imperial constellations (imperiale Ordnungen), which places his work firmly within the current popular historiographical trend of what has been called Mediterraneanism. He defines this concept as follows (220-221): "Eine imperiale Ordnung lässt sich als ein Komplex aus Ressourcen, Strukturen und Konzeptionen groβräumiger Herrschaft begreifen." Such a constellation ("einen übermachtigen Herrschaftsverband") furthermore needs to meet six criteria: 1. outstanding military, economic or sacral potential; 2. great wealth; 3. sea power; 4. real and enduring dominion; 5. a wide sphere of influence; 6. sectoral hegemony in a substantial part of the Mediterranean.
The link between the first part (on "Kaisertum") and this second part is not made altogether clear, apart from the fact that Burkhardt is somehow fascinated by the self-evident observation that medieval emperors in spite of their theoretical universalist aspirations were not always more powerful than other contemporary rulers who did not possess any imperial titles. His selection of examples (or "Realtypen") of Mediterranean imperial constellations only adds to the confusion (224-240): both the Byzantine (before 1204) and Holy Roman (under Henry VI and Frederick II) empires, the Norman kingdom of Sicily, the Italian seafaring city states of Venice and Genoa, unnamed "arabischen Herrschaften des Mittelmeerraumes"; and to a lesser degree also: the Spanish kingdoms, the kingdom of Jerusalem, the kingdom of France (under Saint Louis), the papacy, and the "Nachfolgereiche" in the Byzantine space after 1204 (including the Latin Empire).
This list would appear to include most of the major powers in the 12th/13th century Mediterranean. However, why for example the kingdom of Cyprus is omitted, or the Seljuk sultanate of Rum, or the city state of Pisa, remains unexplained. Also, to put inter alia Genoa, the papacy, the Byzantine empire and the kingdom of Jerusalem in the same analytical category seems questionable, since it is obvious that these do not meet the stated criteria in the same way or to a comparable degree. Burkhardt does not even take the time to seriously argue how the selected powers would meet his criteria. For example his discussion of the Norman kingdom barely takes up half a page (227). Another example: how Venice or Genoa meet the criterion of "weiträumigen Herrschaft" (yet "das zentrale Kennzeichen, das imperiale Ordnungen von allen anderen Herrschaftsverbänden unterscheidet, ist ihr Bezug zu einer weiträumigen Herrschaft" (234)), goes unexplained. Both were certainly important economic powers and developed a network of points of support across the Mediterranean (including direct rule over islands such as Crete), but whether this constitutes "weiträumigen Herrschaft" seems very debatable.
Burkhardt next zooms in on the Latin Empire of Constantinople (241-369). This is the most problematic part of his work. There would appear to be two crucial issues. The first being that he has limited himself to the use of a narrow selection of original sources and modern literature, often preferring outdated or popularizing studies over more recent or thorough works, which in the end hypothecates many of his interpretations and conclusions. Although his bibliography looks impressive and includes most of the relevant titles (381-456), the text itself of his chapters and the critical apparatus tell a markedly different story. Burkhardt also deemed it not necessary to include a solid introduction into the available source material, which is regrettable since the preservation of documents is very unbalanced indeed and a factor to be reckoned with (for example virtually no sources concerning the internal imperial administration have been preserved, while documents concerning Venetian interests are relatively abundant, which at first sight creates an impression of Venetian dominance). A second problem is that Burkhardt's analysis is often confined to only the first few years of Latin imperial rule from Constantinople or to a single incident, but in his interpretation--implicitly or explicitly--extrapolates his findings to the entire period 1204-1261. The quote from Friedrich Wilken's Geschichte der Kreuzzüge (1832!) with which Burkhardt begins his analysis pretty much sets the tone for what follows: "einem Reiche welches in seinem Einrichtung und Verfassung den Kern des Verderbens trug" (257). One could not use a more clichéd point of departure.
His discussion of the religious and ecclesiastical situation in Latin Romania is perfunctory. Unexplainable is that the major studies on this topic by inter alia Robert L. Wolff, Jean Richard, Michael Angold and Tommaso Violante remain completely absent from his analysis and footnotes.  Ernst Gerland's monograph from 1905(!) on the Latin Empire under its first two emperors (1204-1216) is on the contrary cited continuously (and not only here, but throughout the entire book).  Gerland's book to be sure is still valuable, but it is inevitably outdated in many respects. Moreover Burkhardt's treatment of Latin-Byzantine relations in the religious/ecclesiastical sphere or of the internal affairs of the Latin patriarchate of Constantinople (patriarchal election, ecclesiastical possessions, relationship between spiritual and secular authorities, etc.) are practically confined to the opening years (circa 1204-1214), with hardly a word being devoted to the following decades, which did bring evolution and change.
Burkhardt's views on the relationship between the Latin emperors and the other political powers (Western princes, barons and lords; Venice and its officials; Byzantine magnates and functionaries; etc.) within the empire, which were feudally dependent upon them, are likewise deficient, as they are essentially based on again Gerland and also Peter Lock's rather popularizing book on the Latin Aegean (up until the 15th century), which includes only a rather concise and not always very convincing section on the period 1204-1261.  Recent or more fleshed-out studies containing new insights or a more nuanced approach by for example David Jacoby, Benjamin Hendrickx or Guillaume Saint-Guillain are virtually neglected.  His discussion of the relationship between the emperor and his vassals is practically limited to the conflict between Baldwin I and marquis Boniface of Montferrat over Thessaloniki in 1205 and the so-called Lombard rebellion in 1209 against emperor Henry, which itself is marred by the fact that Burkhardt's has missed crucial recent contributions.  Furthermore, Burkhardt attaches too much importance to the Latin Empire "constitutional treaties" of 1204-1205 (which outlined a theoretical division of power between the interested parties), without bothering to analyze whether subsequent political realities conformed with these purely normative texts (which in important respects was not the case).
The listed shortcomings have as inescapable consequence that most of Burkhardt's interpretations and conclusions concerning the nature and workings of the so-called Latin Empire (with regard to imperial ideology, Latin-Byzantine relations, the internal balance of power, etc.) should be treated with great caution. Finally, also his reiterated emphasis on the "Multiplizität von Kaisern" after 1204 which would have been responsible for "grundlegenden Veränderungen von Konzeptionen des Kaisertums" (372) is ill-founded: although there indeed were several claimants to the Byzantine imperial throne after 1204 calling themselves emperors (in Constantinople, in Nicaea, in Epiros, in Trebizond, and even in Tirnovo), there nevertheless was still only one (Christian) empire in the Eastern Mediterranean, and both in Western Europe or in the Byzantine space only one of these claimants was seen as the legitimate emperor; and such strife between different claimants to the same (imperial) throne was really nothing new (though the specific circumstances of course were).
Students of medieval empires/emperorship in the Christian world may find in Burkhardt's book a starting point or introduction into this field of research. But even here, with his strong focus on the virtuality or hybrid nature of the concept and reality of medieval empire, Burkhardt fails to address a vital question: if empires and an emperor's imperial power were essentially virtual, than why did these empires and emperors nevertheless continue to exist or to be restored? Why could the medieval Christian world apparently not do without at least one or two emperors or empires? Obviously the continued existence of an empire and an emperor was crucial to the medieval world view. And not just of any empire or emperor, but of the Roman empire and emperor. Perhaps this providing of continuity with the classical past (where lay the origins of Christianity), and not its virtuality, should rather be seen as the essence of medieval Kaisertum.
1. Robert Lee Wolff, "The Organization of the Latin Patriarchate of Constantinople 1204-1261: Social and Administrative Consequences of the Latin Conquest," Traditio 6 (1948): 33-60; idem, "Politics in the Latin Patriarchate of Constantinople," Dumbarton Oaks Papers 8 (1954): 228-303; Jean Richard, "The Establishment of the Latin Church in the Empire of Constantinople (1204-1227)," The Mediterranean Historical Review 4 (1989): 45-62; Michael Angold, Church and Society in Byzantium under the Comneni (1081-1261) (Cambridge: Cambridge University Press, 1995, second edition 2006); Tommaso M. Violante, "Innocenzo III e l'Oriente bizantino," Nicolaus 24 (1997): 311-352.
2. Ernst Gerland, Geschichte der Fremdherschaft in Griechenland. Bd. 2. geschichte des lateinischen Kaiserreiches von Konstantinopel. Teil 1. Geschichte der Kaiser Balduin I. und Heinrich 1204-1216 (Homburg vor der Höhe: Selbstverlag, 1905)
3. Peter Lock, The Franks in the Aegean, 1204-1500 (London: Longman, 1995).
4. A few essential titles: David Jacoby, La féodalité en Grèce médiévale. Les "assises de Romanie", sources, application et diffusion (Paris: Mouton, 1971); idem, "The Encounter of Two Societies: Western Conquerors and Byzantines in the Peloponnesus after the Fourth Crusade," American Historical Revue 78 (1973): 873-906; idem, "The Venetian Presence in the Latin Empire of Constantinople (1204-1261): The Challenge of Feudalism and the Byzantine Inheritance," Jahrbuch der Östterreichischen Byzantinistik 43 (1993): 141-201; idem, "The Greeks of Constantinople under Latin Rule 1204-1261," in The Fourth Crusade: Event, Aftermath, and Perceptions. Papers from the Sixth Conference of the Society for the Study of the Crusades and the Latin East, Istanbul, Turkey, 25-29 August 2004, ed. Thomas F. Madden (Aldershot: Ashgate, 2008), 53-73; idem, "From Byzantium to Latin Romania: Continuity and Change," Mediterranean Historical Review 4 (1989): 1-44; Benjamin Hendrickx, "Les institutions de l'empire latin de Constantinople (1204-1261): Le pouvoir impérial (l'empereur, l'impératrice, les régents)," Byzantina 6 (1974): 85-154; idem, "Les institutions de l'empire latin de Contantinople (1204-1261): la cour et les dignitaires," Byzantina 9 (1977): 187-217; idem, "Le contrat féodal et le fief dans l'empire latin de Constantinople," Byzantiaka 20 (2000): 223-242; Guillaume Saint-Guillain, "Deux îles grecques au temps de l'empire latin. Andros et Lemnos au XIIIe siècle," Mélanges de l'école française de Rome. Moyen Âge 113 (2001): 579-620; idem, "Seigneuries insulaires: les Cyclades au temps de la domination latine (XIIIe-Xve siècle)," Médiévales. Langues, textes, histoire 47 (2004): 31-45; idem, "Comment les Vénitiens n'ont pas acquis la Crète: note à propos de l'élection impériale de 1204 et du partage projeté de l'Empire byzantin," Travaux et Mémoires 16 (2010): 713-758.
5. Benjamin Hendrickx, "Boniface de Montferrat et Manuel Angelos, empereur "manqué" de Byzance (1204)," Byzantinos Domos 12 (2001): 71-75; Thomas F. Madden, "The Latin Empire of Constantinople's Fractured Foundation: The Rift between Boniface of Montferrat and Baldwin of Flanders," in The Fourth Crusade: Event, Aftermath, and Perceptions. Papers from the Sixth Conference of the Society for the Study of the Crusades and the Latin East, Istanbul, Turkey, 25-29 August 2004, ed. T. Madden (Aldershot: Ashgate, 2008), 45-52.