Map of Asia in 400 AD (400 CE)

The Sasanian Empire, officially Eranshahr, was an Iranian empire that was founded and ruled by the House of Sasan from 224 to 651 AD. Lasting for over four centuries, the length of the Sasanian dynasty's reign over ancient Iran was second only to that of the Arsacid dynasty of Parthia which immediately preceded it.

Mapped extent in 400 CE: 2.99M km²

The Jin dynasty or the Jin Empire, officially Jin, sometimes distinguished as the Sima Jin or the Two Jins, was an imperial dynasty in China that existed from 266 to 420 CE. It was founded by Sima Yan, posthumously known as Emperor Wu of Jin, who previously served as the regent of the Cao Wei dynasty.

Mapped extent in 400 CE: 2.44M km²

The Gupta Empire was an Indian empire during the classical period of the Indian subcontinent which existed from the mid 3rd century to mid 6th century CE. At its peak, the dynasty ruled over an empire that spanned much of the northern Indian subcontinent.

Mapped extent in 400 CE: 1.99M km²

The Byzantine Empire, also known as the Eastern Roman Empire, was the continuation of the Eastern part of the Roman Empire centred on Constantinople during late antiquity and the Middle Ages. Having survived the fall of the Western Roman Empire in the 5th century AD, it endured until the fall of Constantinople to the Ottoman Empire in 1453.

Mapped extent in 400 CE: 1.76M km²

The Huns were a nomadic people who lived in Central Asia, the Caucasus, and Eastern Europe between the 4th and 6th centuries CE. According to European tradition, they were first reported living east of the Volga River, in an area that was part of Scythia at the time.

Mapped extent in 400 CE: 1.44M km²

The Protectorate of the Western Regions (simplified Chinese: 西域都护府; traditional Chinese: 西域都護府; pinyin: Xīyù Dūhù Fǔ; Wade–Giles: Hsi1-yü4 Tu1-hu4 Fu3) was an imperial administration (a protectorate) situated in the Western Regions administered by Han dynasty China and its successors on and off from 59 or 60 BCE until the end of the Sixteen Kingdoms period in 439 AD. The "Western Regions" refers to areas west of Yumen Pass, especially the Tarim Basin in southern Xinjiang.

Mapped extent in 400 CE: 597,725 km²