The most reputable place to find legacy Age of Empires II mods and campaigns is Age of Kings Heaven (AOKH) . It is a long-standing community archive.
This is a fan-made campaign created many years ago. Because it is older community content, it is generally available for free as it was never a commercial product. The Trasamire Campaigns Free Download
Searching for a free download of typically points toward a specific campaign or module for the classic real-time strategy game Age of Empires II (likely the Age of Kings or The Conquerors editions). The most reputable place to find legacy Age
Only download from established community hubs like heavengames.com or ModDB . These sites have been the standard for decades. The Trasamire Campaigns Free Download
Go to the "Custom Campaigns" menu in-game to play.