東羅馬帝國存在了一千多年，文化相同，這麼長的時間了，為什麼沒有像中國一樣，成為一個統一的民族？

比如拜占庭族或者居士坦丁堡族，

補充提問，我的意思是中國很久就是一個文化一個文明了都是漢族人，，再沒有出現民族內鬥的矛盾，為什麼現在巴爾幹半島號稱歐洲火藥桶呢？

首先在討論前現代的政治實體時請盡量避免使用「民族」這種概念，「民族」與「民族主義」本身是現代基於前現代某些並未定型的族群概念構建出來的較為定型的政治與文化概念。在這種意義上不但東羅馬，中國也不存在一個「統一」的「民族」。

其次東羅馬存不存在一個擁有相同認同感、政治標籤的共同體？毫無疑問是存在的，並且是一個相當接近現代民族國家語境下定義的共同體，這個共同體的名字是「羅馬人」。

看見 @黯天 關於東羅馬身份認同感的回答中有這樣一句話。

不管是希臘人，還是亞美尼亞人，亦或是斯拉夫人，只要生活在帝國的疆界之內，無不自豪地宣稱自己是「羅馬人」。

這個說法是在把「羅馬人」這個概念從「族群意識」這個層面上剝離出來，而將其定義為一個超族群的國族概念。的確在狄奧多西一世的設計下「羅馬人」的確是一個非族群概念，而是作為全羅馬帝國正統基督徒的認同：

EMPERORS GRATIAN, VALENTINIAN AND THEODOSIUS AUGUSTI. EDICT TO THE PEOPLE OF CONSTANTINOPLE.

It is our desire that all the various nations which are subject to our Clemency and Moderation, should continue to profess that religion which was delivered to the Romans by the divine Apostle Peter, as it has been preserved by faithful tradition, and which is now professed by the Pontiff Damasus and by Peter, Bishop of Alexandria, a man of apostolic holiness. According to the apostolic teaching and the doctrine of the Gospel, let us believe in the one deity of the Father, the Son and the Holy Spirit, in equal majesty and in a holy Trinity. We authorize the followers of this law to assume the title of Catholic Christians; but as for the others, since, in our judgment they are foolish madmen, we decree that they shall be branded with the ignominious name of heretics, and shall not presume to give to their conventicles the name of churches. They will suffer in the first place the chastisement of the divine condemnation and in the second the punishment of our authority which in accordance with the will of Heaven we shall decide to inflict.

GIVEN IN THESSALONICA ON THE THIRD DAY FROM THE CALENDS OF MARCH, DURING THE FIFTH CONSULATE OF GRATIAN AUGUSTUS AND FIRST OF THEODOSIUS AUGUSTUS[4]

—?Codex Theodosianus, xvi.1.2

但是制度設計幾乎絕大部分情況下都不等於現實。在具體實施上，每個人使用該詞的時候往往在定義上都有出入，甚至是較大的出入。在每個具體情況下「羅馬人」所指代的東西都未必相同。這裡我舉一些常見的，看起來比較「通用」的羅馬人定義出來作為例子，然後說一下這些概念為什麼不總是正確：

1.「羅馬人」是塞薩洛尼基敕令中所說的全體信奉正教的帝國臣民：

這個明顯不適用於斯拉夫人。實際上東羅馬就算重新收回北色雷斯之後，也沒有把保加利亞人當做是「羅馬人」，當地的保加利亞人也沒有記載大面積認為自己是「羅馬人」。例如十一世紀的一位主教有以下的話語：

One such pure Roman, Theophylaktos Hephaistos, appointed their bishop in the late eleventh century, argued that the Bulgarians were no longer a barbarian ethnos but a people of God, civilized and yet distinct from the Romans.

十一世紀末時東羅馬是完全統治保加利亞的，而保加利亞人名義上的確也都是正教徒，但是在Theophylact的話語體系中保加利亞人仍然不能等同於「羅馬人」。他們的確是「不同於野蠻人」，因為他們接受了基督教，但是他們也不是「羅馬人」。

如果說保加利亞人是因為不忠於東羅馬而不被認為是羅馬人，那麼在額我略·帕庫良（Gregorios Pakourianos）的例子中完全不是如此：

A few years after Kekaumenos, another Georgian condottiere, Gregory Pakourianos, who had likewise served the empire faithfully, had risen to the much more exalted post of Grand Domestic of the West and been rewarded with immense landholdings, founded the monastery of Backovo in present-day Bulgaria (1083). While professing his unflinching adherence to the religion of the Greeks, he formally forbids any Greek monks or priests to be enrolled in his monastery because Greeks are grasping and unreliable. Pakourianos died fighting for the empire, but never learnt to sign his name in Greek characters (he did so in Armenian).

帕庫良是一個出生在帝國東部邊境的亞美尼亞軍人，他為帝國南征北戰，並且獲得了極高的榮譽與大量的賞賜，但是他在北色雷斯的修道院里卻明令拒絕希臘人，因為他們「奸詐狡猾」。他在修道院典章上的簽名也是用亞美尼亞語而不是希臘語。

他喬治亞語原文的翻譯：

第一章：

「...... of which I was reckoned worthy, following the tradition of this Georgian race, agreeing and corresponding in all doctrinal tradition with the most orthodox and pious race of the Romans and the great church of God among them......"

他在這裡明顯是把自己和羅馬人區分開的。

第二十三章：

I command all those in the monastery and impress it upon them with a most strict ordinance, that a Greek should never be appointed a priest or a monk in this holy monastery of mine, except only as a notary, knowing how to write and send the opinion of the superior to the rulers of the time and, when sent to the same people by him, he could go and deal with the needs of the monastery. I give this instruction and insist upon it for the following reason, lest [the Greeks], being violent, devious, or grasping, should create some deficiency or cause harm to the monastery or lest they appoint someone opposed to the place and eager to gain control over it or gain for himself the office of superior or appropriate the monastery on some other abominable pretext. These sort of things we have often seen happen among our people, caused by simplicity and a gentle disposition. Otherwise we follow these men in the faith as our teachers and we obey their doctrines.

注意中古喬治亞語中並不區分「羅馬人」與「希臘人」，兩個詞都是Berzdeni，而東羅馬是Saberdzneti「希臘人/羅馬人的地盤」. Pakourianos的原文長這樣：

2. 「羅馬人」是在帝國統治下的、使用希臘語或者拉丁語的正教徒：

普羅科比在戰史中提到過一個小角色：

Among them was Ioannes himself and Aruth, the leader of the Heruls. About a hundred of the Romans perished. Now there had been with Ioannes a certain Gilakios, an Armenian and commander of a small force of Armenians. This Gilakios did not know how to speak either Greek or Latin or Gothic or any other language except Armenian. When some Goths came upon him, they asked him who he was. They were averse to killing every man who came in their way so as not to destroy each other in fighting at night, which could easily happen. But he was able to give them no answer except that he was Gilakios, a general, for his rank, which he had received from the emperor, he had heard spoken many times and had been able to learn it by heart. The barbarians, then, perceiving by this that he was an enemy, made him a prisoner for the while, but not long after put him to death.

這裡的Gilakios將軍是一個亞美尼亞人，在戰爭中被哥特人抓住了。他希臘語、拉丁語或者哥特語都不會說，只能不停重複他自己的軍銜和名字，最後普羅科比說他被「野蠻人」殺死了。如果考慮到Gilakios本人不會希臘語或者拉丁語，他自己也是個「野蠻人」，但是他在這個語境下是作為「羅馬將軍」被「蠻族人」監禁並宰掉了。

而巴爾幹的正教原住民、操通俗拉丁語的弗拉赫人，在東羅馬人的口中卻不是「羅馬人」。十一世紀的Kekavmenos如此記載：

His is the first mention of that ethnic group in Southeastern Europe. While depicting them as an "extremely unfaithful and depraved people," Kekaumenos traced back their lack of loyalty to antiquity and identified the Vlachs with the 「so-called Dacians and Bessi, who used to live near the Danube and Sava rivers, where now the Serbs live, in inaccessible and inhospitable places.」

注意在這裡所說的"extremely unfaithful and depraved people."有語境上的特殊含義。如果你不懂中世紀希臘語，你可能會覺得這裡的people/?θνο? 所說的就是一個ethnic subgroup，而東羅馬是一個multi-ethnic empire，所以他們也是羅馬人。實際上中世紀希臘語中?θνο?這一詞是明確跟ρωμα?ο?對立的，這個詞的用法來自於基督教經文中猶太人與異邦人的對立。當單個拿出來使用的時候，?θνο?一詞有明確的「異族」含義。

3. 「羅馬人」是在帝國統治下的、使用希臘語的正教徒：

你可能以為這是正確答案了，但是遠沒有這麼簡單。君堡城內的貴族往往嘲笑外地人為「蠻族人」，因為他們的希臘語太「土」了。

Italos case also shows that by Annas time there was a very clear hierarchy within the state, whereby those who ful?lled all the political and ethnic criteria of Roman-ness saw themselves as naturally superior, and indeed were in reality socially and economically of the ?rst rank: the elite of the empire were Greek-speaking, Orthodox and imbued with the centuries of tradition of imperial Constantinopolitan rule. For this Constantinopolitan elite, in fact, there was little difference between ethnic others and provincial Romans. The result was that, by the end of the twelfth century, the empire was seriously out of balance in many respects and not least in the division of sentiment between capital and provinces. It is easy to ?nd examples of twelfth-century Constantinopolitan contempt for provincials – Michael Choniates ironic implication that the Athenians are really barbarians, Constantine Manasses disdain for smelly Cypriots and so on.

所以說東羅馬人口中的「羅馬人」到底是什麼？這是一個很複雜的問題，因為在不同的時間、不同的語境下，人們口中「羅馬人」未必有同一個意思。在前現代的個人與社群政治中，身份認同往往是帶有流動性的一個概念，所以需要在單個的場景下分析。

參考資料：

Kaldellis, Anthony.Hellenism in Byzantium: The Transformations of Greek Identity and the Reception of the Classical Tradition. New York: Cambridge University Press, 2011.

Mango, Cyril.The Oxford History of Byzantium. Oxford: Oxford University Press, 2004.

Page, Gill.Being Byzantine: Greek Identity before the Ottomans. Cambridge University Press, 2008.

Prokopios.Wars of Justinian. Hackett Publishing Co, Inc, 2014.

Thomas, John, and Angela Constantinides Hero, eds.Byzantine Monastic Foundation Documents. Translated by Giles Constable. Washington, D.C.: Dumbarton Oaks Research Library and Collection, 2000.

我看有答主寫羅馬的政治制度，認為一直是「聯邦」或者「殖民」，這裡糾正一下。戴克里先時代，行省地位就已經和義大利一樣了，君士坦丁時代更是免除了對羅馬的特別救濟，特別是在基督教普及之後，事實上不再存在「奴役」或者「殖民」的政治制度。至遲在君士坦丁時代，羅馬帝國就已經一個中央集權的龐大帝國，而非「各說各話」的聯邦。

首先要明白一點，民族在近代以前是一個偽概念。所謂的中華民族也不過是梁啟超硬造出來的一個政治概念而已，統一的中華民族絕非自然形成。

那麼，東羅馬帝國一千多年真的什麼都沒有形成嗎？那當然是不可能的，不過形成的不是所謂的「民族」，而是一種「認同感」。

不管是希臘人，還是亞美尼亞人，亦或是斯拉夫人，只要生活在帝國的疆界之內，無不自豪地宣稱自己是「羅馬人」。

這種「認同感」不僅基於輝煌的歷史，也基於先進的文化。東羅馬帝國在漫長的中世紀一直充當著文明的燈塔，保存了古典時代絢爛的文化成果。即使是在帝國文化最黑暗的時刻—七八世紀黑暗時代的文化衰退，羅馬也依然是基督教世界文明的頂峰。

如果你讀過拜占庭帝國時期的作品，你就會發現，幾乎沒有作者不自稱「羅馬人」，拜占庭帝國/東羅馬帝國在他們的筆下都是「羅馬帝國」。他們篤信羅馬文化的優越性，將不接受羅馬文化的其它民族斥為蠻夷。（這點和中國倒是一模一樣嚯嚯嚯）

答主最近正好讀完了馬其頓王朝時期的史詩《狄吉尼斯阿克里特》。書中故事梗概如下：

一個伊斯蘭的埃米爾入侵羅馬帝國，燒殺搶掠無惡不作，卻被一個將軍的女兒俘獲了心神。他在愛情的作用下（實際是被基督文化感召）皈依了基督教，又將自己的族人遷入羅馬，舉族皈依基督教，成為了「羅馬人」。

後來，埃米爾的兒子出世了。他被稱為「混血的邊境之王」（「狄吉尼斯阿克里特」），十二歲就能手撕獅熊，一個人在極短時間內就能幹翻一千多名騎兵（……這大概是用了禁咒）。他不僅娶了杜卡斯家族的女兒，還得到了羅馬皇帝的親切召見。他去世時，無數的人悲哀慟哭。

這個故事能表達什麼？一個無惡不作的魔王能被羅馬文明感召，而這個魔王及其家人在皈依基督教後被承認為羅馬人。他的兒子，一位混血的孩子，得到了羅馬人發自內心的愛戴與支持。

這不是狹隘的「民族」，這是一種與中國古代類似的「文化認同」。你認同我的文化，我就接納你。不管你曾經是阿拉伯人還是法蘭克人，只要你接受羅馬的文化，你就是「羅馬人」。

人家東帝國也有文化同化的，只可惜還沒完成就被打爆了……

舉個例子：小亞內陸的伊蘇里亞人就希臘（羅馬）化的很徹底。斯拉夫人還曾經充斥著巴爾幹，阿提卡北邊一度斯拉夫化，最後還不是被洗回了東正教和希臘（羅馬）文化？

所以拜拜只是時運不濟，不然少說也能洗完巴爾幹和小亞。

所謂同化，事實上是因為技術進步，生產關係改革，兩個不同民族朝著同一個方向發展，最終走向一體。

否則除非人數對比太過懸殊，兩家接觸又太過頻繁，兩個民族從來都不存在同化一說。

也不要高估漢族的同化能力。否則漠北兩千年過去了，直到近代還是游牧民族。臉紅不紅？

中國的民族統一在1919年左右。