Was Crassus an ancient Bill Gates though? Not so much. Rome's wealthiest mostly obtained their fortunes from conquest. Crassus, on the other hand, made his fortune by taking advantage of his peers. For example, during Sulla's dictatorship, Crassus would buy the estates of other citizens after they fell victim to Sulla's proscriptions for pennies on the dollar. He even snuck the names of wealthy individuals onto the proscription lists just so he could plunder their estates! Crassus also, famously, ran a fire brigade that would show up to fires and then refuse to put them out until the owner of the burning property sold out to Crassus for cheap.
For a society of mafia warrior lawyers, the Romans sure let each other get away with murder.