In weekly blog 23 (https://forums.projectceleste.com/threads/weekly-blog-23-caesar-pompey-crassus.4420/), the devs for Project Celeste announced the Roman Triumverate content coming to their rehosting of Age of Empires Online.
The first Roman Triumverate, Caesar, Crassus, and Pompey, have been brought in as new advisor cards for the upcoming Romans civilization (ETA March 2020), as well as part of a new game mode reminiscent of the alliance wars system, which was never carried over in full in the rehosting (the majority of the PvE quests were turned into global quests for everyone to do, and the bonuses and PvP are gone).
This upcoming PvE release will feature this new game mode, and the Romans, as well as a global quest pack, though these 3 may be launched independently of one another come next year due to scope of the additions. This follows several new full scale questing regions and storylines, as well as upscaled event content with their own exclusive rewards. All Romans assets ingame are either unreleased content of the original developers, or freshly designed to suit the civilization theme, with hundreds of man hours put into background historical research in total for the civilization.
Project Celeste brings Age of Empires Online back fully free to play, as a community development project, within the Game Content Usage Rules as specified by Microsoft. Find out about installation here: https://forums.projectceleste.com/threads/installation-guide.12/