So the goal of this thread is, as a community, to collect these sources together to build a single narrative of his life. I originally planned to focus only upon his conquests; but since his life story is so integrally tied to this story, I feel it would be foolish to leave it out. And on the note of his life, we all understand there are different, conflicting narratives about Tiber Septim. These will all be incorporated into a single timeline, one that stands astride both myth and legend. Tiber is both from Atmora and from Alcaire, in other words. Let's not treat anything lightly.
To start, I've collected several sources which I believe will be of use. I encourage the community to contribute more.
http://lagbt.wiwiland.net/wikibiblio/images/4/4c/Obscure_talos-king-atmora.jpg.
http://www.imperial-library.info/content/art-war-magic:
Sedd Mar: Master Arctus advised Tiber Septim before the battle of Five Bridges not to commit his reserves until the enemy was victorious. Tiber Septim said, "If the enemy is already victorious, what use committing the reserve?" To which Master Arctus replied, "Only in victory will the enemy be vulnerable to defeat." Tiber Septim went on to rout an enemy army twice the size of his.
http://www.imperial-library.info/content/attrebus-guard:
Several important events and individuals are mentioned here. The Third Legion, the Moth Rebellion, The storming of Tarak Shan, The pursuit of Reekee's kidnappers, The Sack of Senchal, General Pottreid, the Aldmeri victory at Black Rocks, and the Ruby Legion.
http://www.imperial-library.info/content/amiel-richton-admiral-lord:
Again, several important items. The Richton family and Cuhlecain, the New West Navy, the Battle of Bjoulsae, Admiral Vasi Hadrach and his assassination by Reachmen, and of course the Battle of Hunding Bay.
http://www.imperial-library.info/content/remanada-chapter-2-chevalier-renald-blade-pig:
A few important tidbits. Chevalier Renald's relationship with Cuhlecain and supposed cover to get close to Tiber.
Dialogue from Skyrim:
He's from the battle, I just know it. He's one of Tiber Septim's soldiers... back from the dead.
You don't remember me, Hjalti? Two campaigns we served together. You saved my life time and time again.
Hjalti? I've never heard of anyone named Hjalti. Tiber Septim had many names. Maybe that's one of them?
A sword? I remember a legend that Tiber Septim had attacked one of the enemy camps before he came to Old Hroldan. It could be there.
You promised me, Hjalti. You promised that when we sacked Hroldan, you would make me your sworn brother.
And I've waited. Even after the enemies' arrows dug into my chest and their hammers crushed my bones. I've waited.
Give me your sword, Hjalti. That we may become brothers as you promised.
Remembers our lessons from the sword masters of Alcaire? Let me show you a few things you may have forgotten before we leave Hroldan.
I fought by your side. To take back the Reach from the savages.
Do you think the ghost is one of... Tiber Septim's dead men?
That's right. In the Second Era, Tiber Septim himself led the army that conquered Old Hroldan from the barbarians of the Reach.
Septim would later found the Empire that united Tamriel, but his first known battle and victory was right here.
And this inn has the very bed the great general slept in on his first night as Old Hroldan's liberator. As good as it was hundreds of years ago.
Old Hroldan is the stone that the Empire's history is built on.
Just like Talos himself at the Battle of Old Hroldan, reclaiming the Reach from those heathen natives.
You don't remember me, Hjalti? Two campaigns we served together. You saved my life time and time again.
Hjalti? I've never heard of anyone named Hjalti. Tiber Septim had many names. Maybe that's one of them?
A sword? I remember a legend that Tiber Septim had attacked one of the enemy camps before he came to Old Hroldan. It could be there.
You promised me, Hjalti. You promised that when we sacked Hroldan, you would make me your sworn brother.
And I've waited. Even after the enemies' arrows dug into my chest and their hammers crushed my bones. I've waited.
Give me your sword, Hjalti. That we may become brothers as you promised.
Remembers our lessons from the sword masters of Alcaire? Let me show you a few things you may have forgotten before we leave Hroldan.
I fought by your side. To take back the Reach from the savages.
Do you think the ghost is one of... Tiber Septim's dead men?
That's right. In the Second Era, Tiber Septim himself led the army that conquered Old Hroldan from the barbarians of the Reach.
Septim would later found the Empire that united Tamriel, but his first known battle and victory was right here.
And this inn has the very bed the great general slept in on his first night as Old Hroldan's liberator. As good as it was hundreds of years ago.
Old Hroldan is the stone that the Empire's history is built on.
Just like Talos himself at the Battle of Old Hroldan, reclaiming the Reach from those heathen natives.
Also, take note of the full description of these particular lines.
FFFFFFFF -- -- GetIsID == 1 -- MaleUniqueGhost FreeformOldHroldanB FreeformOldHroldanBCuhlecainBranch Topic PlayerDialogue Custom FreeformOldHroldanBAccept FormID 00079B18 1 FreeformOl_FreeformOldHrol_00079B18_1 Data\Sound\Voice\Skyrim.esm\MaleUniqueGhost\FreeformOl_FreeformOldHrol_00079B18_1.xwm File Not Found I'll find your sword. I long to taste battle again. Anger 50 FFFFFFFF -- -- GetIsID == 1 -- MaleUniqueGhost FreeformOldHroldanB FreeformOldHroldanBCuhlecainBranch Topic PlayerDialogue Custom FreeformOldHroldanBReject FormID 00079B17 1 FreeformOl_FreeformOldHrol_00079B17_1 Data\Sound\Voice\Skyrim.esm\MaleUniqueGhost\FreeformOl_FreeformOldHrol_00079B17_1.xwm File Not Found An old sword? That's a fool's errand. I cannot go into battle without a sword, Hjalti. Anger 50 FFFFFFFF -- -- GetIsID == 1 -- MaleUniqueGhost FreeformOldHroldanB FreeformOldHroldanBCuhlecainBranch Topic PlayerDialogue Custom FreeformOldHroldanBHjaltiBranchTopic FormID 00068198 1 FreeformOl_FreeformOldHrol_00068198_1 Data\Sound\Voice\Skyrim.esm\MaleUniqueGhost\FreeformOl_FreeformOldHrol_00068198_1.xwm File Not Found Hjalti? Who are you talking about? You promised me, Hjalti. You promised that when we sacked Hroldan, you would make me your sworn brother. Sad 50 FFFFFFFF -- -- GetIsID == 1 -- MaleUniqueGhost FreeformOldHroldanB FreeformOldHroldanBCuhlecainBranch Topic PlayerDialogue Custom FreeformOldHroldanBHjaltiBranchTopic FormID 00068198 2 FreeformOl_FreeformOldHrol_00068198_2 Data\Sound\Voice\Skyrim.esm\MaleUniqueGhost\FreeformOl_FreeformOldHrol_00068198_2.xwm File Not Found Hjalti? Who are you talking about? And I've waited. Even after the enemies' arrows dug into my chest and their hammers crushed my bones. I've waited. Sad 50 FFFFFFFF -- -- GetIsID == 1 -- MaleUniqueGhost FreeformOldHroldanB FreeformOldHroldanBCuhlecainBranch Topic PlayerDialogue Custom FreeformOldHroldanBHjaltiBranchTopic FormID 00068198 3 FreeformOl_FreeformOldHrol_00068198_3 Data\Sound\Voice\Skyrim.esm\MaleUniqueGhost\FreeformOl_FreeformOldHrol_00068198_3.xwm File Not Found Hjalti? Who are you talking about? Give me your sword, Hjalti. That we may become brothers as you promised. Sad 50Notice...anything?
Anywho, that's all I'm throwing up for now. I know there are further references in the Pocket Guides as well as in Heresy, so we'll consider those as granted for now.