Byzantine Empire and Sasanian Empire

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. The term 'Byzantine Empire' was coined only after its demise; its citizens used the term 'Roman Empire' and called themselves 'Romans'.

The Sasanian Empire, officially Eranshahr (Middle Persian: 𐭠𐭩𐭥𐭠𐭭𐭱𐭲𐭥𐭩, romanized: Ērānšahr, lit. 'Empire of the Iranians'), was an Iranian empire that was founded and ruled by the House of Sasan from 224 to 651 AD (the era of late antiquity). 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.