Ekpyrosis (//; Ancient Greek: ἐκπύρωσις ekpýrōsis, "conflagration") is a Stoic belief in the periodic destruction of the cosmos by a great conflagration every Great Year. The cosmos is then recreated (palingenesis) only to be destroyed again at the end of the new cycle. This form of catastrophe is the opposite of kataklysmos (κατακλυσμός, "inundation"), the destruction of the earth by water. The destruction of the universe was in the form of fire. The time frame of destruction was never defined or given by any of the Stoics. The fire destruction was to cleanse the universe. The cleansing of the universe was to help create a pure universe. The flames would destroy everything in the universe. Then, everything would be rebuilt in the exact same way in every detail before the fire. After so long, the process by fire would happen again and again. This cleansing of the universe is infinite.
There are three reasons that the belief was taught by the Greeks. The reasons come from the theories of Zeno and Cleanthes. The first cause is that the god of the universe keeps increasing in size making himself have to absorb himself when he gets too large. The second is that the sun and stars burn so hot and bright that they dry out the universe. With everything so dry, it causes the universe to catch fire burning everything up. Zeno states that the fire that destroys the universe will not destroy the very thing that gives itself life, which is the seas. Zeno's thought was to fix the issue caused by the theory of elemental anathymiasis. So the fire would not destroy the sea. The third is that when the planets all return to their position from when the universe was first created, it would also start the process of Ekpyrosis.
The concept of Ekpyrosis is attributed to Chrysippus by Plutarch. Ekpyrosis itself however, was not a universally accepted theory by all Stoics. Other prominent stoics such as Panaetius, Zeno of Tarsus, Boethus of Sidon, and others either rejected Ekpyrosis or had differing opinions regarding its degree. Once such idea is that Ekpyrosis by some was generally viewed as a positive event that would result in a "purification" of the soul and a renewal of all that was destroyed. While another such as the Roman Poet Lucan, depicted Ekpyrosis as just an end with no new beginning, that Ekpyrosis brought about only destruction upon the world. The extent to which Stoics discussed and disagreed regarding Ekpyrosis is largely attributed to works of Hippolytus of Rome, found in the Stoicorum Veterum Fragmenta.
Ekpyrosis itself was, for the most part, a short-lived cosmological theory. With both Zeno of Tarus and Cleanthes theorizing on Ekpyrosis in the third century BC, and then Chrysippus expanding upon this soon after in the second century BC, Ekpyrosis would begin to be abandoned altogether by early Roman Stoics as early as the first and second centuries BC. A strong acceptance of Aristotle's theories of the universe, combined with a more practical lifestyle practiced by the Roman people, caused the later Stoics to focus their main effort on their own social well-being on earth, not on the cosmos.
A prime example are the Stoic-influenced writings of the Roman Emperor Marcus Aurelius (121–180). In his Meditations, he chooses to discuss how one should act and live their life, rather than speculate on cosmological theories.