Army mysteriously vanished

[Amaris]

Hi,

In my current game as SPQR Epirus conquered the whole balkan peninsula, and after I took Segesta from the Eleutheroi Epirus went to war with me.
I had two almost full stack armies in the Segesta region and one of them was attacked and outnumbered by an epirote full stack army. I saved before the battle and in the end won a heroic victory (my first famous battle in the current game). After saving the game again this army was attacked by another epirote acie and I decided to retreat now. Doing this I could hear my general scream and my legion vanished!
Well....I would have reloaded then, but my other legion in the segesta region was also attacked now and it was quite a violent battle which was hard to win. I didn't want to fight it again, so I didn't reload and abandoned the legion which had won before such a glorious victory. Afterwards I could read that it's general had fallen in battle.

What happened ?
I thought I had retreated !

Why was my army automatically destroyed ???
If the epirotes pursuited my legion and attacked it again, why wasn't I given the chance to fight manually ?

Greetings,
Amaris