The Sassanid Persian Empire (also spelled Sasanid Empire, Sassanian Empire, or Sasanian Empire), known to its inhabitants as Ērānshahr and Ērān in Middle Persian and resulting in the New Persian terms Iranshahr and Iran, is the last pre-Islamic Persian Empire, ruled by the Sasanian Dynasty from CE 224 to CE 651.

The Sassanid Empire, which succeeds the Parthian Empire, is recognized as one of the two main powers in Western Asia and Europe, alongside the Roman Empire and the Byzantine Empire, for a period of more than 400 years.

The Sassanid Empire is founded by Ardashir I, after the fall of the Arsacid Empire and the defeat of the last Arsacid king, Artabanus IV.

During its existence, the Sassanid Empire encompasses all of today's Iraq, Iran, Afghanistan, eastern Syria, the Caucasus (Armenia, Georgia, Azerbaijan, and Dagestan), southwestern Central Asia, part of Turkey, certain coastal parts of the Arabian Peninsula, the Persian Gulf area, and areas of southwestern Pakistan.

The native name for the Sassanid Empire in Middle Persian is Eran Shahr which means Aryan Empire.

According to legend, the vexilloid of the Sassanid Empire is the Derafsh Kaviani.

It is also hypothesized that the transition toward the Sassanid Empire represents the end of struggle of ethnic proto-Persians with their close migrant ethnic relatives, the Parthians, whose original homeland was in modern-day Central Asia.The Sassanid era, during Late Antiquity, is considered to have been one of Persia's/Iran's most important and influential historical periods, and constituted the last great Iranian empire before the Muslim conquest and the adoption of Islam.

In many ways, the Sassanid period witnesses the peak of ancient Persian civilization.

Persia influences Roman civilization considerably during the Sassanid period.

The Sassanids' cultural influence extend far beyond the empire's territorial borders, reaching as far as Western Europe, Africa, China and India.

It plays a prominent role in the formation of both European and Asian medieval art.