The battle was fought by the forces of the Aldmeri Dominion and the Imperial Legion. The defending forces were led by Lord Naarifin, while the assaulting Generals were Decianus, Jonna, and an unknown hero disguised as Emperor Titus Mede II.
The Battle of the Red Ring is named after the Red Ring Road which encircles the Imperial City. The result of the battle was the reconquering of the Imperial City, after it had fallen into the hands of the Aldmeri just one year prior. The battle has since become a point of discussion and reverence among Imperial war strategists.
After "The Sack of the Imperial City" in 4E 174, the Aldmeri Dominion believed the Empire's surrender to be inevitable, and close at hand. Emperor Titus II allowed this notion to continue unchallenged until 4E 175, when he set in motion a plan to take back the Imperial City. The legions of General Decianus had been long on their return from Hammerfell, and upon arrival, took cover in the Colovian Highlands outside of Chorrol. Their presence remained undetected by the Aldmeri, and they initiated battle with a devastating surprise attack. Meanwhile, General Jonna led a garrison of mostly Nord soldiers to a rally point at Cheydinhal. They fought their way along Red Ring Road in an assault lasting two days, the plan being to join with the forces of Decianus while the Emperor planned to lead a third army in full assault from the north. 
However, shortly before the battle, the Emperor was wounded by a assassins, and was too weak to lead the attack. Realizing the importance of his presence at the battle, the Emperor charged an unknown hero with wearing his armor, leading the attack on the city, and defeating Lord Naarifin.
Despite resistance from Aldmeri reinforcements from both Bravil and Skingrad, Jonna's Nords succeeded in holding the road, while the forces of Titus II were free to drive into the city, and retake the capital, thus ending a battle that spanned five long days. The battle effectively destroyed the main army of the Dominion in Cyrodiil.
A few legends surround this battle. One is that Emperor Titus II wielded Goldbrand during the battle. In reality, it was wielded by Reive, Naarifin's Daedric minion, and retrieved by The Forgotten Hero who used it in the battle. Others are centered around the death of Lord Naarifin. There are accounts of him being hung from the White-Gold Tower for thirty-three days before being carried off by a winged Daedra. In reality, he was absorbed into Oblivion by the Daedra he served in life, and his corpse was consumed by an Oblivion Gate.
This was the last significant battle of the Great War. Directly afterwards, the Empire signed the White-Gold Concordat, thus ending the war in the favor of the Aldmeri Dominion. Some take this battle as proof that the Empire could stand against the Dominion, and should have fought on, while others would argue that it greatly exhausted resources. Either way, it was instrumental to the outcome of the war.