The Sasanian or Neo Persian Empire was founded in 224 when Ardashir I overthrew the existing Parthian regime. The empire centered on modern day Iran and Iraq and was to exist until 651 when it in turn would be overthrown by Islamic invaders. It was one of leading world powers and an arch rival of the Roman-Byzantium empire for over 400 years.
The Sasanians saw themselves as the natural successors to the Achaemenid Persians who had been defeated by Alexander the Great. It was therefore their duty to reconquer all lands in the middle East that had been lost to Western powers. This brought them into conflict with Rome.
Perhaps its greatest king was Shapur the great who reigned from 240 -270 AD. He is known for defeating three invading Roman armies and after the infamous battle of Battle of Edessa he captured the Roman emperor Valerian whom he then lead around in chains and after he died had him skinned and preserved.
For 400 years the Sasanian Empire was the major power in the Near East as the rival of the Late Roman Empire. Not only that, but they sustained relations with the Tang Dynasty of China and several Indian Kingdoms where their products and culture were held in high esteem.