The Drop Site Massacre

The Drop Site Massacre was one of the most infamous betrayals of the Horus Heresy, a meticulously planned slaughter that gutted the loyalist cause in a single treacherous stroke. It unfolded on the black sands of Isstvan V, where seven Space Marine Legions had been dispatched to bring the traitor Warmaster to heel.

The loyalist assault came in two waves. The first, comprising the Iron Hands, Salamanders, and Raven Guard, made planetfall and drove hard against Horus's dug-in forces, expecting the second wave to reinforce them. But the four Legions of that second wave, the Night Lords, Iron Warriors, Word Bearers, and Alpha Legion, had already gone over to Horus. As the first wave pressed the attack, their supposed allies opened fire from behind, trapping them between two enemies.

The result was carnage. The loyalists were shattered, the Iron Hands' primarch Ferrus Manus slain by his own turned brother, and only scattered survivors escaped the killing ground. Three proud Legions were reduced to a fraction of their strength, crippled for the remainder of the war. The massacre revealed the full scope of Horus's treachery and demonstrated the cold, calculating cruelty at the heart of the rebellion. It stands among the darkest days chronicled in the Horus Heresy, a wound from which the loyalist Legions never fully recovered.