Early career

Sima Rui was born in 276 in the Jin capital of Luoyang as the son of Sima Jin (司馬覲), who was the heir to the Princedom of Langya, and his wife, Xiahou Guangji (夏侯光姬 Xiàhóu guāng jī). According to an alternative account at the end of his biography in the Book of Jin, Sima Rui may have been the product of an affair between Lady Xiahou and a minor official from the family of the Cao Wei general, Niu Jin. Sima Rui's grandfather Sima Zhou, Prince of Langya and uncle of Emperor Wu of Jin, died in June 283, leaving Sima Jin to inherit the princedom, with Lady Xiahou becoming Princess Consort. Sima Jin died on 9 March 290 at the age of 35 (by East Asian reckoning), and Sima Rui became the Prince of Langya. The Book of Jin referred to him as steady and dexterous.

About two months after Sima Rui became Prince of Langya, Emperor Wu died. Emperor Wu's successor, Emperor Hui, was developmentally disabled, and he was under the control of various regents throughout his reign. As the struggle to become Emperor Hui's regent (known as the War of the Eight Princes) grew in intensity, Sima Rui was humble in his dealings, and kept himself aloof from political developments in order to protect himself. His ability to hide his talents meant that most people were unaware of them. However, Ji Shao (嵇绍 Jī Shào; son of Ji Kang), who was then Palace Attendant, saw that Sima Rui was special. He said to others, "The Prince of Langya has an extraordinary appearance, which does not belong to that of a subject."

In 304, in the midst of the War of the Eight Princes, Sima Rui joined Sima Yue, the Prince of Donghai, and his campaign against Sima Ying, the Prince of Chengdu, as a minor general. After Sima Ying defeated Sima Yue, Sima Ying executed Sima Rui's uncle Sima Yao (司馬繇 Sīmǎ yáo), the Prince of Dong'an, on 18 September. He decided to flee back to his principality, Langxie (roughly modern Weifang, Shandong), under counsel of Sima Yue's assistant Wang Dao, whom he befriended during the campaign. He first attempted to head back to Luoyang, but when he was about to cross the Yellow River, he was stopped by guards who were instructed to stop any nobles or high level officials from crossing; Sima Ying had ordered such, fearing that nobles would desert him or plot against him. His own guard Song Dian (宋典 Sòng diǎn) then arrived and shoved him under the ruse that they were both construction workers. The guards then allowed them to cross. After Sima Rui got to Luoyang, he took his mother, Princess Dowager Xiahou, and headed to Langxie where they spent the next few years away from the War of the Eight Princes.

In August 307, Sima Yue had emerged victorious in the aftermath of the War of the Eight Princes as the regent for Emperor Huai (Emperor Hui's successor and half-brother) seven months earlier. Under the advice of his wife Princess Pei, he commissioned Sima Rui as the military commander of parts of Yang Province (揚州 Yángzhōu, modern Zhejiang and southern Jiangsu and Anhui) south of the Yangtze River, with his post at Jianye. Prior to his appointment, the region had been under the control of the rebel general, Chen Min from 305 to 307. Many of the southern gentry clans initially backed Chen Min, but towards the end, they became discontented with his rule and returned to Jin by overthrowing him. Within his first year at Jiangdong, his mother Princess Dowager Xiahou died.

Among Sima Rui's staff, Wang Dao was entrusted by him as a chief advisor. As Sima Rui lacked fame, after he arrived in Jianye, few of the gentlemen from the southern gentry clans would come visit and support him. Under Wang Dao's counsel, Sima Rui personally visited He Xun (賀循 Hè xún; great-grandson of He Qi) and Gu Rong (顧榮 Gù róng; grandson of Gu Yong) and invited them to serve in his administration. He and Gu were well regarded by the local population, which eventually began to trust Sima Rui's leadership. Wang Dao and his cousin, the general Wang Dun, served in key roles, and it was said at the time that the ___domain was ruled equally by the Simas and the Wangs.

While Sima Rui was in the south, Sima Yue was preoccupied in quelling rebellions and fighting the Han-Zhao dynasty in the north. Sima Rui was essentially out of Sima Yue's reach, but for the first few years, he had to keep in check with the commander, Zhou Fu, who controlled Yang province north of the Yangtze. The deadlock was finally broken in February 311, when Zhou Fu, under fire by the imperial court for suggesting that they move to his base in Shouchun, was forced into rebellion. Sima Rui, now with grounds to attack Zhou Fu, ordered his forces to march north of the Yangtze and annexed the rest of Yang province.

After the fall of Luoyang

In July 311, not long after Sima Yue died in April, Luoyang fell to Han forces and Emperor Huai was captured during the Disaster of Yongjia. A high-ranking minister, Xun Fan was able to escape Luoyang and founded a provisional government near the former capital. Through Xun Fan's assent, Sima Rui began to exercise more imperial power as he was acclaimed the leader of the Jin alliance and granted special authority to appoint and dismiss chief officials. With many officials fleeing south of the Yangtze, Wang Dao advised Sima Rui to scout for and recruit the talented men the northern emigres families to serve in his administration. All in all, Sima Rui was able to pick out more than a hundred officials from the northern emigres, and they were collectively known as the "106 Officials".

South of the Huai river and to the west of Sima Rui, the Inspector of Jiang province (江州 Jīangzhōu, modern Jiangxi), Hua Yi and the Inspector of Yu province (豫州 Yùzhōu, modern central Anhui at this time), Pei Xian both outrightly refused to acknowledge Sima Rui's new authority. In response, the prince sent Wang Dun to campaign against them, killing Hua and forcing Pei to flee before replacing them with his own followers. In the central Yangtze region, the two provinces of Jing (荊州 Jīngzhōu, modern Hubei) and Xiang (湘州 Xiāng zhōu, modern Hunan) had long been struggling with a refugee crisis, due to many people fleeing from the ongoing war with the Cheng-Han dynasty in Sichuan. These refugees, mainly led by Du Tao, eventually rebelled in 311, ousting the Inspector of Xiang and repeatedly defeating the Inspector of Jing, Wang Cheng. Sima Rui took the opportunity to further expand his influence into the central Yangtze, installing his own Inspector of Xiang and convincing Wang Cheng to give up his office. Under the command of Wang Dun and other generals such as Tao Kan and Zhou Fang, the agrarian rebels resisting Jin rule in Jing and Xiang were gradually subjugated.

Though Sima Rui had initially relied on the southern gentry clans to consolidate his rule in the Jiangnan, he eventually began relying more on the northern emigres families as they continued to flock to him. The southern gentry were divided on his shift of trust; while most were willing to tolerate it, others such as Zhou Qi from the Zhou clan of Yixing became resentful towards the northern emigres. The hardliners rallied around Zhou Qi and his family to oust the northern emigres and force Sima Rui to restore the southern clans to power. However, their conspiracies in 313 and 315 were both exposed and did not garner enough support, thus failing to have a major impact on Sima Rui's stance.

In 313, after Emperor Huai was executed by the Han, Sima Ye, a nephew of Emperor Huai, was declared emperor (posthumously known as Emperor Min) in Chang'an. Due to the naming taboo for Emperor Min's given name of "Ye" (業), Sima Rui's headquarters Jianye (建業) was renamed Jiankang (建康), a name it would keep for several centuries. Sima Rui was named the Left Prime Minister, a title that he accepted; however, he took no actual actions in aid of the emperor. Indeed, even when Sima Yue was still alive, the prince showed little interest in lending his forces to help pacify the north. When his general and the refugee leader, Zu Ti requested to lead an army north, he gave Zu only supplies for one thousand men with no actual troops; Zu had to seek out his own soldiers, but was eventually able to recover a number of cities south of the Yellow River.

In 316, Chang'an fell to Han forces, and Emperor Min was captured. Sima Rui quickly declared that he was going to act against Han, but then quickly claimed a lack of supplies and cancelled the campaign. In spring 317, his officials requested that he take the throne. After he declined initially, he took the title "King of Jin"—a title previously used by Sima Zhao and Emperor Wu while they were regents of Cao Wei—rather than emperor on 6 April 317. He created his son Sima Shao crown prince on 1 May of the same year.

Early reign and the loss of Northern China

On 7 February 318, Liu Cong, the emperor of Han Zhao, executed Emperor Min. About two and a half months later, on 23 April, news of Emperor Min's execution reached Jiankang. Sima Rui then declared himself emperor three days later. At this time, the areas directly under his control were roughly south of the Yellow River and east of the Three Gorges, although pockets of Jin territory in the north—chief among which was Youzhou (modern Beijing, Tianjin, and northern Hebei), controlled by the ethnic Xianbei governor Duan Pidi—largely also recognized him as emperor. However, while technically recognizing him as emperor, Zhang Shi the governor of Liang Province (modern central and western Gansu), chose not to use his era names and instead continued to use Emperor Min's era name of Jianxing, thus hinting non-recognition. Additionally, he did not recognize and was non-committal to Sima Bao the Prince of Nanyang's claim for emperor, despite his alliance with his father Zhang Gui and whose ___domain was closely related to the Zhang clan, believing Emperor Yuan would be a more effective emperor but retaining Emperor Min's era name: another sign that the Zhang clan sought independence from the Jin, though not immediately at the time. Later that year, when the Han-Zhao emperor Liu Can was overthrown by his official Jin Zhun who initially indicated that he was submitting to Emperor Yuan's authority, Emperor Yuan tried to take advantage by sending an army to assist Jin Zhun. However, long before the army could get there, Jin Zhun was defeated by the new Han-Zhao emperor Liu Yao and the general Shi Le.

In 319, Duan Pidi's forces fell to Shi Le—who had by that point declared independence from Former Zhao as declared by Liu Yao, establishing Later Zhao in the same year—and Duan fled to another governor still loyal to Jin, Shao Xu the governor of Ji Province (冀州 Jìzhōu, in what is now central Hebei). In the next year, Shi Le sent his generals Shi Hu and Kong Chang to capture Shao. They were successful but Duan Pidi was able to take control of Shao's forces, thus once again leading the resistance in the north. While this was happening, remaining Jin resistance around west of Chang'an (or Northwest China, in this area Emperor Yuan has no control of these forces—instead this is where Zhang Shi (who technically recognized the emperor) has more control) began to falter as they entered internal conflict. Meanwhile, Sima Bao (who had by then declared himself as Prince of Jin in previous year, ostensibly following the steps of Sima Zhao and did not recognize the emperor by this point) apparently suffering famine and facing Former Zhao invasion, tried to escape to Zhang Shi's ___domain but was denied by the force Zhang Shi sent to 'protect' him but whose orders were actually to prevent Sima Bao from entering his ___domain. Failing to rescue himself, he presumably faced resistance by remaining generals under him Yang Tao and Chen An (which had by this point defected to Han-Zhao, but bearing some loyalty to him) and was soon apparently murdered by his generals Zhang Chun (張春 Zhāng chūn) and Yang Ci (楊次 Yáng cì), replacing him with his relative Sima Zhan (since Sima Bao had no sons). Soon after, Former Zhao forces led by Chen An attacked Sima Zhan's ___domain in revenge, killing him and in turn killing Zhang and capturing Yang, ending Jin resistance in the Qin Province.

Later in 320, Zhang Shi was assassinated by his guards Yan She (閻涉) and Zhao Ang, acting from the rumors spread by the magician Liu Hong. Because Zhang's son was still young at the time, his brother and successor Zhang Mao executed Liu Hong and declared a general pardon, effectively declaring his ___domain independent from the Jin. Additionally, Zhang Mao began to use the era name "Yongguang" (永光) internally, while using "Jianxing" as in communications with other states, which is seen as evidence that Zhang Mao's ___domain is effectively independent from the Jin. though he still continues to refer himself as Governor of Liang Province. This action completely ended Jin rule in Northwest China as his ___domain would continue evolving into the vacillating state of Former Liang, especially by the time Zhang Jun ruled the state. By 321, Shao Xu's forces finally collapsed and Duan Pidi was captured by Shi Le, ending his resistance and all resemblance of Jin rule in China north of the Yellow River—although the Xianbei chief Murong Hui the Duke of Liaodong was still in control of modern Liaoning and still considered himself a Jin vassal.

Late reign and confrontation with Wang Dun

By 320, Emperor Yuan's relationship with Wang Dun was at a breaking point, as Wang Dun had grown more and more arrogant and controlling of the western provinces. Emperor Yuan feared him, and therefore began to group men around him who were against Wang Dun as well, such as Liu Huai and Diao Xie (刁協) – men of mixed reputation who, in their efforts to suppress the Wangs' power, offended many other people.

In 321, Emperor Yuan commissioned Dai Yuan (戴淵) and Liu with substantial forces, claiming that they were to defend against Later Zhao attacks, but instead was intending to have them defend against a potential Wang Dun attack. The general who actually had a charge of protecting Later Zhao attacks remains held by Zu Ti. By this time, he was a governor of Yu Province under Jin. Zu Ti was popular with the people he governed, was successfully held off attacks from Later Zhao. The next year, Chen Chuan defected and Zu was defeated but Shi was not able to advance further. In the end, this led into a stalemate, and then informal détente in which peace and trade relations are instituted with Yellow River as the border. When Zu Ti died, there was no one on the Jin side checking the Later Zhao expansion against Jin. After Zu Ti died, the balance of power in the region often vacillated between the Jin and Zhao clans; other players include Cao Ni, a renegade general who ruled Qing Province, and Xu Kan, the general who ultimately surrendered to Jin. Both often had a history of conflicts with the Jin, and both was defeated very quickly by Later Zhao general Shi Hu. Because of these reasons, Jin was unable to hold onto these territories between the Yellow and Huai Rivers and gradually lost them. By the time Cao Ni died, it is likely that Jin does not have any of these territories left; thus these lands were lost for decades until their recovery by Huan Wen during the reign of Emperor Mu of Jin.

In spring 322, Wang Dun started his campaign against Emperor Yuan, claiming that Emperor Yuan was being deluded by Liu and Diao, and that his only intent was to clean up the government. He tried to persuade Gan Zhuo, the governor of Liang Province (what is now northwestern Hubei and southeastern Shaanxi) and Sima Cheng the governor of Xiang Province to join him, and while both resisted, neither was effective in their campaigns against his rear guards. Wang quickly arrived in Jiankang, defeating Emperor Yuan's forces and entering and pillaging Jiankang easily. Liu fled to Later Zhao, while Diao, Dai, and Zhou Yi (周顗) were killed. Emperor Yuan was forced to submit and grant Wang Dun additional powers in the west. Wang Dun, satisfied, allowed Emperor Yuan to remain on the throne, and personally withdrew back to his home base of Wuchang. His forces then defeated and killed Sima Cheng, while a subordinate of Gan's, acting on Wang's orders, assassinated Gan.

After his defeat, Emperor Yuan grew despondent and ill, and died in January 323. Crown Prince Shao succeeded to the throne as Emperor Ming.

Era names

• Jianwu (建武): 6 April 317 – 26 April 318

• Taixing (太興): 26 April 318 – 3 February 322

• Yongchang (永昌): 3 February 322 – 22 April 323

Family

Consorts and issue

• Empress Yuanjing, of the Yu clan (元敬皇后 虞氏; 277–312), personal name Mengmu (孟母)

• Empress Dowager Jianwenxuan, of the Zheng clan of Xingyang (簡文宣皇太后 滎陽鄭氏; d. 326), personal name Achun (阿春)

　• Sima Huan, Prince Dao of Langxie (琅邪悼王 司馬煥; 317–318), fifth son

　• Sima Yu, Emperor Jianwen (簡文皇帝 司馬昱; 320–372), sixth son

　• Princess Xunyang (尋陽公主; b. 323)

　　• Married Xun Xian of Yingchuan (潁川 荀羨; 322–359) in 336

• Jieyu, of the Shi clan (婕妤 石氏)

　• Sima Chong, Prince Ai of Donghai (東海哀王 司馬衝; 311–341), third son

• Cairen, of the Wang clan (才人 王氏)

　• Sima Xi, Prince Wei of Wuling (武陵威王 司馬晞; 316–381), fourth son

• Lady, of the Xun clan (豫章君 荀氏; d. 335)

　• Sima Shao, Emperor Ming (明皇帝 司馬紹; 299–325), first son

　• Sima Pou, Prince Xiao of Langxie (琅邪孝王 司馬裒; 300–317), second son

Ancestry

生平

父親司馬覲於太熙元年（290年）去世後，司馬睿在翌年以十五歲之齡襲封琅邪王。襲爵後司馬睿卻遭遇到八王之亂開始，面對一段朝政混亂時期，司馬睿就表現得謙恭退讓，以圖逃避災禍，又因行事低調，當時也沒太多人注意到他。元康二年（292年）司馬睿拜員外散騎常侍。到了永安元年（304年）時，司馬睿已升為左將軍，並參與討伐成都王司馬穎的蕩陰之戰；但此戰由司馬穎獲得勝利，被帶著親征的晉惠帝被俘，戰前勸司馬穎投降的司馬睿叔父東安王司馬繇更被殺。司馬睿恐懼禍及自身，便逃返洛陽（今河南省洛陽市）接母親一同回到封國琅邪。

永興二年（305年），東海王司馬越起兵討伐在長安（今陝西西安）挾帝掌政的河間王司馬顒，就假司馬睿為輔國將軍；不久司馬越統兵西進，加司馬睿平東將軍、監徐州諸軍事，讓他留鎮下邳（今江蘇省邳州市）。在下邳期間，司馬睿就請了昔日在洛陽力勸自己返回封國的王導擔任自己的司馬，並讓他為自己出謀劃策。永嘉元年（307年），司馬睿聽從王導及東海王妃裴氏的建議，將駐地由下邳遷至東吳故都建鄴（今江蘇省南京市），並獲晉懷帝進為假節、安東將軍、都督揚州江南諸軍事。但司馬睿初到建鄴時未得江南士族禮敬，整整一個月都無人來訪，在王導及王敦的協助下終在江南士族中建立起聲望，司馬睿亦因而選任顧榮、賀循等江南士族領袖為僚佐，與王導、刁協等僑姓士族合作治理江東。司馬睿雖為皇族，然全因著王導、王敦而得江東人擁戴，遂為當時人稱「王與馬，共天下」。

永嘉四年（310年）十一月，鎮東將軍周馥以洛陽孤危，上書請晉懷帝遷都壽春（今安徽省壽縣），此舉因未有先詢問過主政的太傅司馬越而令對方大怒。周馥早前派了淮南太守裴碩領兵赴司馬越以應付對方對二人的徵召，此時裴碩就宣稱得到司馬越的密令，讓他討伐擅命的周馥，轉向進攻壽春。裴碩敗予周馥，被逼退守東城並向司馬睿求援，司馬睿遂派了揚威將軍甘卓及建威將軍郭逸領兵進攻壽春。永嘉五年正月，周馥守了十日而敗，出逃項縣為新蔡王司馬確所拘，不久則憂憤而亡。五月又進號鎮東大將軍、開府儀同三司。但六月就發生了永嘉之亂，洛陽失陷於漢趙且晉懷帝被俘，時司空荀藩逃到滎陽並移檄天下，推了司馬睿為盟主。司馬睿以盟主身分承制改易江州官員任命，但向來以洛陽懷帝政府尚在而拒絕接受司馬睿命令的江州刺史華軼再次不聽命，司馬睿便派王敦統領甘卓、周訪、宋典及趙誘等軍討伐華軼，華軼領兵積極抵抗，卻在衞展及周廣擔任內應之下遭到突襲，兵敗被殺。永嘉六年（312年），晉懷帝在漢趙都城平陽（今山西省臨汾市）被殺，消息在建興元年（313年）四月傳到長安後晉愍帝以皇太子即位為帝，並在五月壬辰日（6月27日）進侍中、左丞相、大都督陝東諸軍事，與大都督陝西諸軍事的右丞相南陽王司馬保分陝而治。建興三年（315年）進位丞相，大都督中外諸軍事。

建武元年（317年），在上一年漢趙俘擄晉愍帝的消息隨平東將軍宋哲傳到建康後，宋哲宣稱有愍帝詔命以司馬睿總攝萬機，西陽王司馬羕為首的眾官員則請司馬睿登帝位，在司馬睿拒絕之下依魏晉兩朝先例改稱晉王，並於建康備百官，立社稷，並改元「建武」。同年晉愍帝被殺，消息在翌年（318年）傳到建康，百官勸進，司馬睿遂即帝位，改元「太興」。即位之時百官在旁，司馬睿特別請一手協助他移鎮江東並取得江南士族支持的王導和他一起同坐御座，惟王導推辭。

永昌元年（322年），大將軍、荊州牧王敦於武昌起兵，以誅劉隗為名進攻建康。司馬睿其實早就提防王敦，尤其前一年就派戴淵以征西將軍出鎮合肥（今安徽省合肥市）、劉隗以鎮北將軍鎮淮陰（今淮安市淮陰區）作外援，聞王敦起兵後便召他們入衞建康，並以王導為前鋒大都督，自己亦親身披甲在城郊檢閱六軍，積極抵抗。然而王敦兵臨建康時即攻石頭城，守城的周札開門迎敵，王敦遂控制石頭城。司馬睿隨後命令諸軍進攻石頭城，為王敦所敗。司馬睿無力抵禦王敦，只好妥協，王敦遂自授丞相主政。逼於王敦的司馬睿憂懼成疾，在同年閏十一月己丑日（323年1月3日）去世，時年四十七歲，葬建平陵，廟號中宗，諡元皇帝。

治理江東

南北形勢

司馬睿移鎮後南方時有的亂事：永嘉四年（310年）建威將軍錢璯作亂陽羨縣、建興元年（313年）在湘州起事，影響荊江湘三州的杜弢及在竟陵郡舉事作亂的杜曾。建興三年（315年）殺吳興太守袁琇的徐馥及在宣城郡舉事的吳末帝族人孫弼圖響應周勰的報復行動。這些變亂而在僑姓和吳姓士族力量的協助及支持下，司馬睿遣軍將之一一討平，以穩定當地。

與南方積極經營相比，司馬睿南鎮建康後北方仍然陷於戰亂之中，洛陽、關中地區及北方諸鎮接連遭漢趙及石勒部隊所攻。司馬睿專心經營南方，雖在晉愍帝被俘後北方諸鎮領袖如劉琨、段匹磾、邵續、段部及慕容鮮卑等皆聯名上表司馬睿勸進以示支持，司馬睿亦曾發檄文北伐，但終未有出兵北征；而有北伐志向的祖逖自請北伐亦得不到支持，司馬睿僅給了一千人的糧食及三千匹布作為物資，讓祖逖自行募兵, 連兵器和盔甲都沒有提供。祖逖努力招撫及進攻下成功收復黃河以南領土，並讓原本在徐兗豫一帶與外族作戰的各個晉將勢力如李矩、趙固、郭默等都和睦共處，受祖逖節度；連石勒也因祖逖而不敢南侵。祖逖以功勳獲當時已稱帝的司馬睿晉升為鎮西將軍，但朝廷仍著眼於與琅邪王氏有關的士族衝突中，甚至為提防王敦而在太興四年（321年）讓戴淵以征西將軍、都督司兗豫並雍冀六州諸軍事出鎮作外援。祖逖本來就對朝廷內士族衝突影響接著對河北之北伐而憂心成疾，現在更派了戴淵來都督自己，更令其不快，終在同年去世。祖逖的位置由其弟祖約接手，但祖約不得眾心，無法繼承其北伐事業，王敦之亂時石勒更趁勢南侵，祖約因無法抵抗而南退，河南領土得而復失。

平抑士族

司馬睿所依仗的王導出身僑姓望族琅邪王氏，他除了成功讓江南士族與司馬睿合作外，亦調和了其他南來的僑姓士族人士，讓他們安心奉戴這個江南朝廷。但其實僑姓士族在朝中仍具主導起位，加上僑姓士族對江南士族的排擠，令到江南士族人士很不忿。其中江南擁巨大勢力的義興周氏領袖周玘雖然有三定江南之功，但仍感在朝中影響力遭僑姓士族壓制，且司馬睿亦顧忌其強盛的地方勢力。周玘就與一些遭到僑姓士族欺侮的人陰謀誅除掌政的僑姓士族，改以戴淵及周玘輔以江南士族執政。但陰謀難產，風聲卻為司馬睿所聞知，司馬睿未有加罪，但短時間三度改調周玘官職，並進其爵為公，這令周玘怒而得病離世，但遺命兒子周勰為他向僑姓士族報仇。周勰及後便聯結徐馥等人謀亂，但因得不到叔父周札支持而失敗，失意而終。但由於義興周氏的聲望及地方勢力，司馬睿未有加罪，至王敦之亂時周氏仍是一門五侯的盛極情形，王敦一直忌憚周氏，遂在錢鳳勸說殺了周札及其親族。吳郡陸氏的陸玩亦輕視時主政的僑姓士族，並拒絕王導的聯姻請求。琅邪王氏雖然功勳卓著，王導與司馬睿關係非純君臣而王導堂弟王廙更是司馬睿的姨表弟，但其實司馬睿移鎮後一直在提防琅邪王氏一族的勢力太盛，威脅其司馬氏的統治權威，遂親任劉隗及刁協，推行自己主張的「用申韓之術」、「以法御下」的方針，其中就有打擊士族的部分，如劉隗就曾連番表奏琅邪王氏王含的胡作非為，又以淳于伯判刑過重至死為理由彈劾出身義興周氏之丞相從事中郎周莚為首的屬官「不勝其任」，逼令王導也自求引咎辭職。後汝南周氏的周嵩門生傷人，並襲擊前來處理的建康左尉，劉隗就因而彈劾周嵩兄周顗「縱肆小人，群為凶害」，讓周顗被免官。司馬睿即位後，劉、刁二人得重用，繼續在司馬睿同意下推行一系列崇上抑下，排抑豪強的「刻碎之政」，其中更包括徵發士族擁有的奴和僮客為兵組建劉隗、戴淵出藩作援的軍事力量, 如此種種反引起南北士族很多不滿和怨恨，其中王敦更厭惡劉、刁二人的行動，終起兵叛亂。

僑州郡縣

八王之亂開始後中原大亂，一些北方人陸續南遷避亂，司馬睿為安撫並管理這些南遷人口，遂僑置了一些州郡縣，如在原屬揚州境內的京口僑置兗州、在荊州僑置新興郡及河東郡、揚州宣城郡的春穀縣僑立本屬豫州的襄城郡及繁昌縣、吳郡的海虞縣北邊僑置徐州的東海郡並置郯、朐及利城三縣，東海餘縣如祝其及襄賁就寄治晉陵郡的曲阿、屬丹陽郡的江乘縣置懷德縣安置自封國琅邪隨自己南鎮的千餘戶人，隸琅邪郡，又置東平及蘭陵郡；自晉陵郡武進縣設立臨淮、淮陵及彭城這些徐州僑郡，又在徐州僑置司州的頓丘郡。此為僑州郡縣之始，及後東晉及南朝皆有設置和改易僑州郡縣之舉。

身世佚聞

• 司馬睿為司馬覲與王妃夏侯光姬所生的兒子，故為晉朝宗室，然而東晉孫盛《晉陽秋》中就稱曹魏時有預言書《玄石圖》有「牛繼馬後」的記載，這令司馬懿設計毒殺了將領牛金以避免預言實現，但稱夏侯光姬和小吏牛欽私通，生下司馬睿，以司馬睿本當姓牛而應預言。《晉書·元帝紀》文末所載亦大致一樣，稱司馬睿是夏侯光姬與牛氏小吏私通所生，魏收在修《魏書》更直接說司馬睿是牛金和夏侯光姬的私生子。

評價

• 唐代房玄齡於《晉書》的「史臣曰」評論說：「晉氏不虞，自中流外，五胡扛鼎，七廟隳尊，滔天方駕，則民懷其舊德者矣。昔光武以數郡加名，元皇（案：晉元帝）以一州臨極，豈武、宣餘化，猶暢於琅邪，文、景垂仁，傳芳於南頓？所謂後乎天時，先諸人事者也。馳章獻號，高蓋成陰，星斗呈祥，金陵表慶。陶士行擁三州之旅，郢外以安；王茂弘為分陝之計，江東可立。或高旌未拂，而遐心斯偃，回首朝陽，仰希乾棟，帝猶六讓不居，七辭而不免也。布帳綀帷，詳刑簡化，抑揚前軌，光啓中興。古首私家不蓄甲兵，大臣不為威福，王之常制，以訓股肱。中宗失馭強臣，自亡齊斧，兩京胡羯，風埃相望。雖復《六月》之駕無聞，而《鴻雁》之歌方遠，享國無幾，哀哉！」

• 唐代某貴族「公子」與虞世南的對話：「公子曰：『中宗值天下崩離，創立江左，俱為中興之主，比於前代，功德云何？』先生曰：『元帝自居藩邸，少有令聞，及建策南渡，興亡繼絕，委任宏茂，撫綏新舊，故能嗣晉配天，良有以也。然仁恕為懷，剛毅情少，是以王敦縱暴，幾危社稷，蹙國舒禍，其周平之匹乎？』」

家世

嗣父

• 晉武帝 司馬炎

妃嬪

• 虞孟母，追封元敬皇后

• 宮人荀氏，生司馬紹、司馬裒，335年卒

• 鄭阿春，生司馬煥、司馬昱、尋陽公主，326年卒，追封宣太后

• 石婕妤，生司馬衝

• 王才人，生司馬晞

子女

• 晉明帝 司馬紹（299年－325年）

• 琅邪孝王 司馬裒（300年－317年）

• 東海哀王 司馬沖（311年－341年）

• 武陵威王 司馬晞（316年－381年）

• 琅邪悼王 司馬煥（317年－319年）

• 晉簡文帝 司馬昱（320年－372年）

• 尋陽公主，嫁荀羨

影視形象

• 電視劇《書聖王羲之》（未播出）：趙文瑄 飾

• 電視紀錄片《中國》第一季（2020年）：滕文浩 飾

注釋