Hey, guys, quick question- is it possible to join the Dark Brotherhood in the first Elder Scrolls game? I have not played it, but I need to know for something I'm writing.

I know that it's and option in all the other games, except Morrowind where you can join Morag Tong instead, but I don't know about the first one.

It is not possible to join any faction in Arena. In fact, as far as I can tell, the Dark Brotherhood doesn't even exist outside of dialog.

In fact, the only faction present in the game at all is the Mage's Guild, and even then, it only serves as a place to buy spells, potions, and magic items, and to use the Spellmaker.