Battle of Beta-Garmon
The Battle of Beta-Garmon, also known as the Great Slaughter of Beta-Garmon, was a battle of the Horus Heresy.
The battle was waged towards the end of the Heresy in 013.M31 following the infiltration of the Alpha Legion in the Solar System in preparation for Horus's advance on Terra. Waged on the strategically important world of Beta-Garmon which was known as the gateway to Sol, the battle became one of the largest of the Heresy. The traitor fleet was led by Horus himself. Primarch Rogal Dorn ordered the defense of the system and sent many of the Imperial Fist from Terra to join the fight.
Ultimately, Horus was victorious and was able to move on the Sol System, culminating in the Siege of Terra.