Themesazon (Greek:μεσάζων,romanized: mesazōn,lit. 'intermediary') was a highdignitary and official during the last centuries of theByzantine Empire, who acted as the chief minister and principal aide of theByzantine emperor. In the West, the dignity was understood as being that of theimperial chancellor (Latin:cancellarius imperii).^[1]

The term's origins lie in the 10th century, when senior ministers were sometimes referred to as themesiteuontes (μεσιτεύοντες), i.e. 'mediators' between the emperor and his subjects (cf.paradynasteuon). The title first became official in the mid-11th century, when it was conferred onConstantine Leichoudes, the futureecumenical patriarch of Constantinople.^[2] In theKomnenian period, it was awarded to senior government officials who functioned asde facto prime ministers, such as theepi tou kanikleiou and thelogothetes ton sekreton, but had not yet acquired a permanent and specific function, nor the power that would characterize it in later years.^[2][3] Rather, it was a title bestowed on the principal imperial secretary of the moment, who acted precisely as an "intermediary" between the emperor and other officials.^[4][5] This reflected the shift of the Byzantine government under the Komnenoi from the old Roman-style bureaucracy to a more restricted, aristocratic ruling class, where government was exercised within the imperial household, as infeudalWestern Europe.^[6]

The office ofmesazon became formally institutionalized in theEmpire of Nicaea,^[7] where the holder of themesastikion (as the function had become known), served as the Empire's chief minister, coordinating the other ministers.^[6] As the emperor and historianJohn VI Kantakouzenos (r. 1347–1354) records, themesazon was "needed by the emperor day and night".[2] This arrangement was inherited by the restoredPalaiologan-era Empire and continued in use until theFall of Constantinople in May 1453. The office was also used in the same function in the Byzantine courts ofEpirus,Morea, andTrebizond. In the latter case, it acquired the epithetmegas ('great').^[2]

• Constantine Leichoudes, until 1050.
• Theodore Styppeiotes, under EmperorManuel I Komnenos (r. 1143–1180).
• John Axouch, under EmperorManuel I Komnenos
• John Kamateros, under Emperor Manuel I Komnenos.
• Michael Hagiotheodorites, under Emperor Manuel I Komnenos.
• Theodore Maurozomes, under Emperor Manuel I Komnenos.
• Demetrios Komnenos Tornikes, under EmperorJohn III Vatatzes (r. 1221–1254).
• Theodore Mouzalon, until 1294.
• Nikephoros Choumnos, 1294–1305, under EmperorAndronikos II Palaiologos (r. 1282–1328).
• Theodore Metochites, 1305–1328, under Emperor Andronikos II Palaiologos.
• Alexios Apokaukos, 1328–1345, under EmperorsAndronikos III Palaiologos (r. 1328–1341) andJohn V Palaiologos (r. 1341–1391).
• Demetrios Kydones, 1347–1354, under EmperorJohn VI Kantakouzenos (r. 1347–1354); 1369–1383 under Emperor John V Palaiologos; 1391–1396 under EmperorManuel II Palaiologos (r. 1391–1425).
• Demetrios Palaiologos Goudeles, from the late reign of John V Palaiologos toc. 1416 under Manuel II Palaiologos[8]
• Hilario Doria, 1390s–c. 1423, under Manuel II Palaiologos[9]^[10]
• Demetrios Chrysoloras, 1403–1408 inThessalonica under EmperorJohn VII Palaiologos.
• John Phrangopoulos, 1428/9 inMorea underdespotTheodore II Palaiologos
• George Doukas Philanthropenos, 1430–1439.
• Demetrios Palaiologos Kantakouzenos, 1434/5–1448 under EmperorJohn VIII Palaiologos (r. 1425–1448).
• George Doukas Philanthropenos andManuel Iagaris Palaiologos, 1438–1439, while accompanying Emperor John VIII Palaiologos to Italy.
• Loukas Notaras, 1434–1453, lastmesazōn of the Byzantine Empire under Emperors John VIII Palaiologos andConstantine XI Palaiologos (r. 1449–1453).

• Angold, Michael (1975).A Byzantine Government in Exile: Government and Society under the Laskarids of Nicaea, 1204–1261. Oxford: Oxford University Press.ISBN 978-0-19-821854-8.
• Bartusis, Mark C. (1997).The Late Byzantine Army: Arms and Society 1204–1453. Philadelphia, Pennsylvania: University of Pennsylvania Press.ISBN 0-8122-1620-2.
• Beck, Hans-Georg (1955). "Der byzantinische "Ministerpräsident"" [The Byzantine 'Prime Minister'].Byzantinische Zeitschrift (in German).48 (2):309–338.doi:10.1515/byzs.1955.48.2.309.S2CID 191483710.
• Haldon, John F. (2009). "The State – 1. Structures and Administration". InJeffreys, Elizabeth; Haldon, John; Cormack, Robin (eds.).The Oxford Handbook of Byzantine Studies. Oxford, United Kingdom: Oxford University Press.ISBN 978-0-19-925246-6.
• Halecki, Oskar (1930).Un Empereur de Byzance à Rome. Warszawa: Towarzystwo Naukowe Warszawskie.
• Kazhdan, Alexander, ed. (1991).The Oxford Dictionary of Byzantium. Oxford and New York: Oxford University Press.ISBN 0-19-504652-8.
• Loenertz, Raymond-Joseph (1960). "Le chancelier impérial à Byzance au XIVe et au XIIIe siècle" [The imperial chancellor in Byzantium in the 14th and 15th century].Orientalia Christiana Periodica (in French).26:275–300.
• Magdalino, Paul (2002) [1993].The Empire of Manuel I Komnenos, 1143–1180. Cambridge: Cambridge University Press.ISBN 0-521-52653-1.
• Oikonomidès, Nicolas (1985)."La chancellerie impériale de Byzance du 13e au 15e siècle" [The Imperial Chancery of Byzantium from the 13th to the 15th Centuries].Revue des études byzantines (in French).43:167–195.doi:10.3406/rebyz.1985.2171.
• Raybaud, Léon-Pierre (1968).Le gouvernement et l'administration centrale de l'empire byzantin sous les premiers Paléologues (1258-1354) [The government and central administration of the Byzantine Empire under the first Palaiologoi (1258-1354)] (in French). Éditions Sirey.
• Trapp, Erich; Beyer, Hans-Veit; Walther, Rainer; Sturm-Schnabl, Katja; Kislinger, Ewald; Leontiadis, Ioannis; Kaplaneres, Sokrates (1976–1996).Prosopographisches Lexikon der Palaiologenzeit (in German). Vienna: Verlag der Österreichischen Akademie der Wissenschaften.ISBN 3-7001-3003-1.
• Verpeaux, Jean (1955). "Contribution a l'étude de l'administration byzantine: ὁ μεσάζων" [Contribution to the study of Byzantine administration: ὁ μεσάζων].Byzantinoslavica (in French).16:270–296.

• Heads of government
• Byzantine administrative offices

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