So Catiline was this patrician, a decadent SOB who, when mistreated and challenged by the Roman establishment, organized the Roman deplorables and started a rebellion.
It was squashed of course, but for Blok, he remained a hero. Blok calls Catiline the Roman Bolshevik, and insists on approaching him not from Cicero's moralizing NYT-like perspective, but from the perspective of World Revolution.
For Blok, as he puts it, the heart of the Roman Empire stopped when Christ was born. It continued for another few hundred years, but in a zombie-like state until its petty, militaristic, provincial, materialistic character was finally exposed as the bluff it always was, and it collapsed under the weight of its own corruption. And here is Blok's paradoxical view: Catiline's rebellion makes sense only from this perspective.