A peculiar understanding of the nature of justice, in some respects very close to the idea of Fiat justitia et ruat coelum; the idea that justice must be done no matter the consequences. On the one hand, this is a very admirable goal - the ends of justice should not be politicised or corrupt, and often it's a court's prerogative, and arguably duty, to take the unpopular decision that is judged to be legally correct. Piso's justice, depending on how you look at it, is taking this idea to such an extreme that either you specifically disregard any notion of morality beyond the letter of the law, or just plain revel in executing it cruelly. This sort of thing has been discouraged for a while; there's a comparatively well-known quote by the Elizabethan jurist Sir Edward Coke to the extent that 'Lex Anglite est lex misericordite'. And while experience may teach us that the practise can fall short of the ideal, by and large we recognise the need to temper the punitive aspects of justice with humanity.
The Romans didn't go in for that sort of thing, as every schoolboy knows. We refer here to Seneca's De Ira, in which he relates a story about a Roman governor named Gnaeus Piso; 'a man free from many vices,
but misguided, in that he mistook inflexibility for firmness'. A soldier comes back to camp after having gone AWOL - or whatever the Latin equivalent of that is. However, he doesn't have the other soldier, with whom he went AWOL, with him. Piso orders the returned soldier executed, because he must have murdered his comrade. No sooner has the soldier put his head on the chopping block, when the missing man appears. Naturally, the centurion in charge calls off the execution, and takes the two men before Piso.
Piso's justice is this; he orders the first soldier executed, because he was sentenced to death. He orders the second soldier executed for causing the death of the first by not showing up with him. And then he orders the centurion executed for not doing his duty in executing the first soldier.
Seneca had a moral lesson in there, of course, but the real moral is this: Romans were not nice people.