In the Warp, Horus's consciousness had been trapped for a million years.
Of course, that "million years" was only the span of time he had subjectively experienced.
In the Materium, perhaps only a few dozen minutes had passed, or perhaps a few hours. But in the Warp, a dimension without any concept of time, Horus's consciousness had endured a million years of loneliness, struggle, interrogation, and torment.
He had seen the same scenes countless times: the Emperor's face turning from loving to indifferent, his brothers' smiles turning from sincere to false, the Imperium's future turning from bright to dark.
He had heard the same whispers countless times. Those voices told him over and over that he was nothing but a pawn, a tool, a worthless thing to be discarded once he had served his purpose.
He had felt the same pain countless times—the pain of betrayal, abandonment, and rejection, like countless needles piercing his soul at once, tormenting him again and again without giving him a moment's respite.
At last, Horus could hold out no longer.
His mental Defense Line, that barrier built from conviction, pride, and will that had sustained him for decades, finally developed its first crack after a million years of relentless assault.
At first, the crack was tiny, like a hairline fracture in porcelain, but it soon began to spread, branching out like a spiderweb across his entire mental Defense Line.
He could feel his will slipping away, like sand falling between his fingers. No matter how hard he tried to grasp it, he could not stop it from draining away.
The power of the Four Gods seized upon that weakness.
Those four figures, those beings that had been circling him, whispering and waiting all this time, sensed the instant Horus's mental Defense Line collapsed.
They