Thomas Palaiologos (or Palaeologus) (Greek: Θωμάς Παλαιολόγος, Thōmas Palaiologos) (1409 – 12 May 1465) was Despot in Morea from 1428 until the Ottoman conquest in 1460. After the desertion of his older brother to the Turks in 1460, Thomas Palaiologos became the legitimate claimant to the Byzantine throne. Grandgrand father of Ivan the Terrible.
Thomas Palaiologos was the youngest surviving son of the Byzantine Emperor Manuel II Palaiologos  and his wife Helena Dragaš. His maternal grandfather was Constantine Dragaš. His brothers included the Byzantine emperors John VIII Palaiologos and Constantine XI Palaiologos, as well as Theodore II Palaiologos and Demetrios Palaiologos, Despots of the Morea, and Andronikos Palaiologos, Despot of Thessalonica. As youngest son, Thomas was never expected to reign, but his children became the only surviving heirs of the defunct Palaiologan dynasty.
Like other imperial sons, Thomas Palaiologos was made a Despot (despotēs), and from 1428 joined his brothers Theodore and Constantine in the Morea. After the retirement of Theodore in 1443, he governed together with Constantine, until the latter became emperor (Constantine XI) in 1448. Thomas remained Despot of the Morea, but was forced to share the rule with his older brother Demetrios from 1449. The Byzantine holdings in Morea had expanded considerably at the expense of the Latin Principality of Achaea. After the last war in 1430 virtually the entire peninsula was under Byzantine rule, and Thomas married Catherine Zaccaria, the daughter of the last Prince of Achaea Centurione II Zaccaria, succeeding to his father-in-law's possessions in 1432.
After this period of success, the fortunes of Byzantine Morea declined, as the collegiate government by several brothers caused increasing friction. This became especially acute after the arrival of Demetrios, who took a pro-Ottoman stance as opposed to Thomas' pro-western orientation. From 1447 the Despots had become vassals of the Ottoman Sultan. At the onset of the siege of Constantinople by Mehmed II of the Ottoman Empire, an Ottoman army was sent with orders to raid in the Morea, preventing help from being sent to The City. After the conquest of Constantinople by Mehmed II on May 29, 1453, to maintain the status quo, the Sultan ordered the two brothers to continue as joint rulers in Morea.
This order had been accepted for the first two years because of the Kantakouzenos family's revolt which started in 1453 during the fall of Constantinople by Demetrius I Kantakouzenos' grandchild Manuel. Only in the next year did the forces of the Palaiologos brothers destroy the rebel forces.
In these circumstances, and without Constantine XI to maintain peace in the family, Thomas sought western support against both the Ottomans and his competitive pro-Ottoman brother Demetrios. He allied with Genoa and the Pope, and defeated Demetrios, who fled seeking help from the Ottomans in 1460. The Ottoman army duly attacked Morea and quickly breached the Hexamilion wall across the Isthmus of Corinth, which was too long to be effectively manned and defended by Thomas' forces. Thomas escaped with his family to Italy, where he had already been recognized as the legitimate heir to the Byzantine Empire at Rome.
The commanders of the garrisons of the fortified cities in Morea, deserted by their rulers, chose individually whether to fight or surrender, depending on their own will and circumstances. In 1460 in the final battle of the Roman Empire in its Byzantine incarnation, Graitzas Palaiologos, the military commander of the city of Salmenikos, defeated Mehmed II, who after a month of siege returned home without conquering that "unimportant city". In the following year Graitzas received an offer to become general of the Republic of Venice, which he accepted, thus leaving Salmenikos to the Ottomans.
After the fall of Morea, Thomas lived in Rome, recognized throughout Christian Europe as the rightful Emperor of the East. To create greater support for his situation Thomas changed his religion to Catholicism in his last years of life. After his death in 1465, the position of rightful Byzantine emperor fell to his older son Andreas Palaiologos, born in Mistra around 1453.
Mehmed II conquered the Empire of Trebizond, de facto the last free territory of the ancient Roman state, in the year 1461. Nevertheless, Mehmed had already proclaimed himself "Roman Emperor" upon capturing Constantinople in 1453.
In an effort to reunite the Catholic Church and the Orthodox Church, Pope Paul II arranged in 1472 a marriage between the Catholic daughter of Thomas, Zoe Palaiologina (renamed Sophia), and Grand Prince Ivan III of Russia, with the hope of making Russia a Catholic country. This attempt to unite churches failed. Nonetheless, because of this marriage, Moscow began in the following century its imperial policy of "third Rome". Moreover, Thomas' great-grandson was Ivan IV of Russia, the first emperor (tsar) of Russia to be crowned as such (the imperial title had already come into use under Ivan III and his son Vasili III of Russia). The last known descendant of Zoe/Sophia was Maria of Staritsa, wife of Livonia's king Magnus . She died in 1610.
By his marriage with Catherine (Caterina) Zaccaria of Achaea, Thomas Palaiologos had at least four children:
- Helena Palaiologina, who married Despot Lazar II of Serbia.
- Andreas Palaiologos, who succeeded as claimant to the Byzantine throne
- Manuel Palaiologos.
- Zoe Palaiologina (renamed Sophia), who married Grand Prince Ivan III of Russia
- George Sphrantzes, The Fall of the Byzantine Empire, trans. Marios Philippides, Amherst MA: University of Massachusetts Press, 1980. ISBN 0 87023 290 8
- Jonathan Harris, Greek Émigrés in the West, 1400-1520, Camberley: Porphyrogenitus, 1995. ISBN 1 871328 11 X
- Jonathan Harris 'A worthless prince? Andreas Palaeologus in Rome, 1465-1502', Orientalia Christiana Periodica 61 (1995), 537-54
- Donald M. Nicol, The Immortal Emperor, Cambridge University Press, 1992. ISBN 0 521 41456 3.
- Oxford Dictionary of Byzantium, Oxford University Press, 1991.
- Steven Runciman, The Fall of Constantinople 1453, Cambridge University Press, 1965. ISBN 0 521 09573 5
- Portraits 
- Signature 
- ^ The Oxford handbook of Byzantine studies, Elizabeth Jeffreys, John F. Haldon, Robin Cormack, Oxford University Press, 2008, p.292
- ^ History of the Byzantine Jews: a microcosmos in the thousand year empire, Elli Kohen, University press of America, 2007, p.156
- ^ Empire of magic: medieval romance and the politics of cultural fantasy, Geraldine Heng, Columbia University Press, 2003, p.152
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|Offspring of Thomas Palaiologos and Katharina Zaccaria of Achaea (1411-1462)|
|Helena Palaiologina (1431-1473)|| |
|Andreas Palaiologos (1453-1502)||1453||1502|| |
|Zoe Palaiologina (c1448-1503)||1448||7 April 1503|| Ivan III Vasilyevich of Russia (1440-1505)|
|Manuel Palaiologos (1455-1512)|
Thomas Palaiologos (c1409-1465)
Palaiologos dynastyBorn: 1409 Died: 12 May 1465
| Despot of the Morea|
with Demetrios Palaiologos
| Succeeded by|
Claimants in exile
|Pretenders to the title|
Constantine XI Palaiologos
|— TITULAR —|
(formally "Emperor of Constantinople")
with Demetrios Palaiologos
* Reason for succession failure *
The Fall of Constantinople led to
the Ottoman conquest of the Byzantine Empire
| Succeeded by|
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