In order to understand the present, we have to look to the past. And there's no past as great as the rise of King Alicorn and the Keepers of Harmony. With love, war, discords, caves, mental institutions-- and, most importantly, the first magical friendship-- it was certainly something Celestia would never forget.
Other stories in the history archives:

The Diary of Diddy Discord
A Slice of ol' Waddle's Life
The Journals of Silas Sombra

This story is based on the Arthurian Legend but it is not imperative that you know everything about it.
In the comments area there will be written links for each new Legend as to how it influences Ponyville as we know it today, and how it is linked to the Arthurian Legends.

Picture courtesy of DreamWings industries (my hand in other words).
Main proofreading done by KartalTheWriter.
Additional proofreading done by Not Worthy and Tyrell the Dragon.
Overview of ideas helped by Samaru163 and KartalTheWriter.

This is a revamped version of the winner of the first Author Support Prompt.