@Bhazor  
In winter Hearth’s Warming, spike states that unicorns used to manage the sun and the moon while describing the roles of the pony tribes.
 
Also, the presence of Cadance, who seemed to grow older in the time between the first flashback we see her in and the wedding, show that Alicorns are not ageless gods.  
We also know that spells that can make you younger can be learned by sufficiently skilled unicorns. This would explain the extreme age of Celestia and Luna.  
This indicates that Alicorns do not wield godlike powers, but have magical skills that can be compared to the most powerful unicorns.  
Infact, Celestia was beaten in a duel of magical might by the changeling queen.
 
Lastly, that Cadance is growing older implies that she must have been born as a foal and is maturing. This along with the nameless alicorn princess from the Love Poison book implies that there are more alicorns around, and that they breed,  
The alicorn foal in the background during Twilights flashback to magical kindergarden seems to support this.
 
From this we can conclude that Alicorns are not godlike, but wield no more power than a unicorn can achive. They are not inherently ageless and breed like any other pony, thus they must be mortal or countless generations of the past would still be around.  
There is nothing godlike about alicorns, in other words.

“before” The reign of Celestia -singular  
not “before” the reign of Celestia and Luna -
 
this is about 50-50 accurate. It mostly depends on whether you want to say HW was pre-discord or post-discord really.

@Bhazor
 
That writers have stated a number of times that Alicorns are suppose to be a mix of ALL THREE races
 
so the alicorn is a symbol of unity between the races
 
Also this is out heancannon crap and you’ve barely even used the information in the episodes.
 
Like why is Heartwarming Eve aka the founding of Equestria takes place AFTER “Equestria’s golden age”
 
There wasn’t an Equestria unit that day!

The Reign of Discord should be an amorphous blob, not a rectangle.

The flag is easy to explain once you read Small Gods by Terry Pratchett. The short version: belief in the alicorns of day and night (who may have been chosen as a symbol of unity among the pony tribes) created Celestia and Luna.

@Bhazor  
No problemo, my good stallion! I get confused all the time!
 
At least that’s what Clover told me when I asked for bells on my robe. Never really understood the girl…

@Background Pony: He got that right. Equestria was founded by six ponies. You could say that they are the elements that get reborn into our heroes.

I think the alicorn flag thing is either  
a) an anachronism like the founding fathers being shown with the modern star spangled banner  
b) my head canon that Celestia and Luna are basically elder gods who were worshipped by ponys for thousands of year before they descended to fight Discord. I mean something must have been controlling the sun before Princess Celstia came to power.
 
 
@ Starswirl
 
I thought you said Discord came before Hearth’s Warming. My mistake.

Deduced from information in the episode? You mean when Spike said, and I quote:“Once upon a time, long before the peaceful rule of Celestia, and before ponies discovered our beautiful land of Equestria, ponies did not know harmony. It was a strange and dark time. A time when ponies were torn apart, by hatred.”

They were lost after Luna was defeated remember?

By using the Elements. We didn’t have them, back before Equestria was founded.

@ Starswirl
 
How could Luna and Celestia defeat Discord then?

Also: Luna remembers how I LOOK. So does Twilight Sparkle, and I definitely never talked to that one.

Also, just because Luna said she knew Starswirl, it doesn’t actually mean she knew him personally. Even if she did, it doesn’t mean that she and Celestia ran the show back then.

What’s all this?
 
No no no, Discord came after Platinum and those other guys founded Equestria. Way way before the rule of Celestia. There were other Alicorns around throughout pony history, where else do you think Cadance came from?
 
Not to mention: Had we the Elements of Harmony at our Disposal back then, do you honestly believe a few measly windigos would’ve been enough to drive us from our homes? Please.

From what I remember, Hearth’s Warming happened before the founding of Equestria.  
The fact that the modern flag was used in the play was most likely because the original flag is not common knowledge, like those American founding plays which have the flag as it is now.

Well Luna remembers Starswirl. And he lived before Hearths Warming eve…

Here we over analyse a children’s cartoon.

What Bhazor said. That seems to be the accepted current timeline.

Hearths Warming is “How Equestria Was Made” so it has to be first. So the united tribes found their kingdom but then they were conquered by Discord. Then Celestia and Luna were born/became alicorns and defeated him, and the united tribes installed the alicorns as rulers. Some time later The Crystal Empire fell and the sisters banished Sombra. Shortly afterwards Luna turned and was banished and then a thousand years later the show starts.

@Ebalosus the pony kinds were united… they lived in the same region and formed a feudal type of society (possibly from lack of celestia being there as monarch) This feudal society broke down around the time of Heart’s Warming.
 
The main thing is that there are alicorns on the first equestrian flag, so even back then they must have known about Luna and Celestia.
 
2. Luna knew Starswirl the Bearded. (Luna Eclipsed) Starswirl was pre-Heart’s Warming

I’m going to agree with igotnopicks and Bhazor here, and state that hearth’s warming eve must’ve taken place before the reign of Discord, because the disparate pony kinds weren’t united.

Deduced- Hearth’s Warming After Discord (A.D)
 
because of the Alicorns on the Equestrian Flag during that time.

Celestia slumber is similar to KING ARTHUR.
 
King Arthur went into a deep sleep, to return when England needed him Most.