Although there isn't much recorded about this period of time, many scholars believe that alot of the great Gods created Tamriel during this time but, didn't leave a record of it for unknown reasons. This era is considered to be many eras fused together in to one huge period of time. But again, that's just one of the many theories. (Dawn Era, Mythic Era, Merethic Era)
The First Era
There are many major events that happened during this era of time. First and foremost, King Harald conquers Skyrim, and immediately renounces Skyrim's ownership by Atmora. Nearly sixty years after that, King Harald dies and the throne is taken over by King Hjalmer. After only one year as king, King Hjalmer dies and his youngest son, Vrage the Gifted takes over for his father. With Vrage the Gifted as king, he leads Skyrim to the conquering of High Rock and Morrowind.
Two years after High Rock and Morrowind fall to Vrage the Gifted, the slave queen Alessia leads her followers in rebellion against the Ayleid controlled White Gold Tower. After she gets some much need assistance from Skyrim, she continues to fight the Ayleids until the Tower finally falls one year later. Alessia then declares herself Empress and leads the new kingdom of humans and the near by Colovian kingdoms. Shortly after, Empress Alessia creates the new religion of the Eight Divines by combining the religions of the Nord and Cyrodiilic tribes. Around this time, the very first Elder Council is forged as well as the first Imperial College of Battlemages.
A short 3 years later; after the Nords conquer what is now modern High Rock, they establish the region's first settlement Daggerfall City. One of the first civilized acts the Nords performed was a census - the so-called Book of Life. This book listed the early laws and guidelines of early colonial life. The final edition was published in the 3rd Century year 401.
The Amulet of Kings is considered to have the most precious gems in all of Cyrodiil. When Empress Alessia was at death's doorstep, Shezarr, the missing sibling god of the Eight Divines, appeared at the White Gold Tower and transformed Alessia into a Cyrodilic saint. She was then given possession of the Amulet for safe keeping. Following these events, the Elder Council elects Belharza the Man-Bull as the second Emperor of Cyrodiil.
Through political maneuvering and questionable machinations, the only known surviving High Elven family, Clan Direnni, rises to power within human lands. Due to Direnni's suspicious activities, Emperor Ami-El joins forces with the Skyrim Empire to mount a full on assault of Clan Direnni in the Western Reach of High Rock.
In the 5th Century, as the Chimer and Dwemer unite, the Nords are finally pushed out of Morrowind (then called Resdayn or Resdaynia) thus allowing the Chimer and Dwemer to finally live in peace. Shortly after, the Skyrim War of Succession ends as the king loses control of High Rock, Morrowind, and Cyrodiil and is never able to regain them.
Nearly two hundred years later, after Vvardenfell mountain erupts, it earns the name Red Mountain and is soon to be the site of a violent and bloody conflict between the once peaceful Chimer and Dwemer. The leaders of both races are killed in the violence which eventually lead to the formation of "modern" Morrowind.
One of the strangest and still unsolved mysteries of Tamrielic lore happened around the same time as the battle of Red Mountain. Simply put, the Dwarven nation in it's entirety, goes missing. This sparks many theories as to what happened but it's thought to have followed their attempt to use the tools on the heart, to make a "superweapon," or to make their race immortal and simply coincided with the war. But the truth is still unknown.
As The First Empire comes to a close with the death of Emperor Reman I, The Second Empire takes over with Emperor Reman II. When Emperor Reman II succeeds in claiming a large part of the swamplands of Argonia, the province of Black Marsh is created. Reman II is killed shortly after and thus ends the reign of The Second Empire. Reman III succeeds to the throne and the First Era comes to a close.
The Second Era
One of the first major events to happen during the Second Era is the formation on the very first Mages Guild. The main purpose of this guild, as specified by the Emperor, is to provide services for the general public. These services included the ability to purchase potions, potion ingredients, magical items, and a selection of standard spells from members within the guild. However, these services were much cheaper for any member of the guild itself. In addition, the guild Steward was permitted to provide members, adventurers, or sometimes mercenaries with certain jobs that benefited the well being of the guild.
In the year 2E283, Akaviri Potentate Versidue-Shaie declares martial law, which lasts for a period of 37 years. During that period, all armies except for that of the Potentate are crushed to avoid any chance of rebellion. This lead to a number of smaller nations uniting with one another to form the province of Elsweyr. Following the destruction of the other armies, Dinieras-Ves "the Iron" founds The Syffim (later known as the Fighters Guild) in order to keep the peace within the provinces. Shortly after, Potentate Versidue-Shaie is assassinated by the Morag Tong. Potentate Savirien-Chorak and all his heirs are also murdered shortly after taking the throne. It's assumed that the Morag Tong are responsible yet again but it's not questioned as the years of the Potentate are now over.
Dagoth Ur and his Ash Vampires awaken after centuries of slumber under Red Mountain and bind themselves to the Heart of Lorkhan. As the Tribunes are bathing themselves in the Heart's power, as they do annually; Dagoth Ur ambushes and drives them off thus rendering him in control of the mountain.
With the death of Emperor Cuhlecain, his general, Tiber Septim begins a campaign to unite all of Tamriel. With the help of the Dwarven artifact Numidium and the battlemage Zurin Arctus Emperor Septim succeeds in his campaign. It is said that Tiber Septim was the greatest emperor Tamriel has ever had; even to this day.
The Third Era
The Third Era starts off very badly for the emperors of Tamriel over the next hundred years. Six emperors and empresses either die of natural causes or are assassinated by The Dark Brotherhood. Finally, things start to settle down. The ninth emperor, Antiochus, takes the throne. Unfortunately, his reign was full of civil wars that even rivaled that of his grandfather Uriel Septim II.
In the year 3E112 Emperor Antiochus dies after a thirteen year reign. His daughter, Kintyra II assumes the throne. Her first cousin Uriel III, accused Kintyra of being a bastard child. After the accusation failed to stop her from becoming Empress, Uriel united disgruntled kings from Skyrim, High Rock and Morrowind and used their forces to coordinate attacks against the Empire. As the Empress was nearby when the attacks began, her bodyguards were overpowered and she was taken prisoner.
With the Empress out of the way and presumed dead, Uriel III leads his entourage of allies to the Imperial City which is overrun in a fortnight. Uriel III then proclaims himself Emperor of Tamriel as Uriel Septim III when in truth, his name was Uriel Mantiarco.
In the year 3E123 Empress Kitarya II is confirmed dead, twelve years after she was kidnapped. The 23rd of Frostfall is now named the day of Broken Diamond in her memory.
After all his trouble, Uriel III ends up getting captured after the battle of Ichidag in Hammerfell. As he's being transported to the Imperial City to stand trial for his war crimes. His carriage is attacked by an angry mob and he's burned alive within the transport.
In the next fifty years, four emperors die natural deaths. Uriel IV takes the throne and rules for nearly fifty years. After his death, his son is disinherited by the Elder Council due to tensions between the council and Uriel IV. The former Nordic king Cephorus II succeeds to the throne.
After years of conflict with a man named Camoran Usurper, emperor Cephorus II is killed in action. Uriel V is sworn in by a weak empire. Almost directly after his coronation, Uriel V begins to invade other provinces and build the empire back into it's former glory. Uriel V builds a reputation that rivals that of Tiber Septim himself as the greatest warrior emperor of Tamriel.
One of the areas that Uriel V invaded was Akavir. This area turned out to be his final resting place. After news of his death had reached the Imperial City, his five year old son was sworn in to the throne. However, due to his age, he did not have full authority over his empire. The Elder Council loved having full, unlimited power to make decisions (and gold) with no one to oppose them. Uriel VI was not given full power to rule until he reached the age of 22 in the year 3E307.
After all the war heroes in Uriel VI's family, he was killed after he fell off his horse. The finest healers and monks in all of Tamriel couldn't fix the damage done to the Emperor. With Uriel VI dead, his sister Morihatha, whom he was very close to, takes the throne.
After nearly fifty years of only operating in Morrowind, the Morag Tong is contracted by rebelling provinces to kill the new Empress. After they succeed, the throne is assumed by Emperor Pelagius IV. His reign lasts a solid twenty-nine years.
With the end of Pelagius IV's reign, Tamriel was closer to unity then ever before. Uriel Septim VII is crowned the next emperor and begins the task of completing Pelagius' work. In the year 3E389, Emperor Uriel Septim VII is betrayed by his Imperial Battlemage Jagar Tharn and is imprisoned in a dimension created by the Battlemage himself.
10 years later, an unknown champion rises up and defeats Jagar Tharn in the dungeons of the Imperial City. With the Battlemage defeated, Uriel Septim VII is freed from his dimensional cell and is reinstated as emperor.
As the immortal Lord High Councilor of House Dagoth, Dagoth-Ur is reawakened in the year 3E427, an ancient Blight disease is awakened as well. This curse last for over 20 years, killing thousands of Morrowind citizens. That very same year, the reincarnation of the Dunmer war hero Nerevar, the legendary Nerevarine arrives in Morrowind by order of the emperor as this hero is destined to defeat Dagoth-Ur and bring peace to Morrowind.
The Tribunal goddess Almalexia loses her divine powers, becomes insane and kills her fellow god, Sotha Sil in the year 3E429. The Nerevarine is enlisted to reforge the Nerevar Indoril's blade, Trueflame, in order to find and kill the powerless, insane former goddess in the Clockwork City.
In the year 3E433 an event occurs that changes the course of Tamriel's future. A secret society called the Mythic Dawn succeeds in the assassination of Emperor Uriel Septim VII and all of his heirs. Following the murder of the beloved emperor, Mehrunes Dagon successfully opens Oblivion Gates all over Cyrodiil and begins an invasion on the humans of the imperial land. A mysterious prisoner is then tasked with the quest to find a hidden and secret heir to the crown.
After this unknown hero successfully locates the hidden heir, a man called Martin, he then rallies eight of the nine cities of Cyrodiil to fight against the demonic soldiers. However, the Daedric had already destroyed the city of Kvatch before the necessary help could arrive.
The Champion of Cyrodiil and heir to the throne, Martin then takes on the form of the Aedric god Akatosh in order to defeat and banish Mehrunes Dagon back to Oblivion. This event marks the end of the Third Era and the beginning of the Fourth.
The Fourth Era
As the Fourth Era has only just began, no one knows for certain what the future holds for Tamriel, but it appears that history is off to an excellent start.
As attacks start to arise by yet another Daedric cult, a curious pilgrim has a vision of the crusader Pelinal Whitestrake and is tasked with reuniting the crusader's relics and reinstating the Knights of the Nine.
The Daedric prince, Lord Sheogorath is cursed and required the assistance of a champion to help him break said curse. This champion succeeds and Lord Sheogorath is allowed to return to his actual form, Jyggalag the Prince of Order. The champion is rewarded with the kingdom of Sheogorath and takes the throne in the Realm of Madness.