Accordingly the constitutional history of Florence resolves itself into a progressive, though chequered, advance of the people against the nobles (or, as they were afterwards called, the magnates) along two lines. In the first place, they had to make the _de facto_ trade organization of the city into its _de jure_ constitution--a movement which culminated in 1282 in the formal recognition of the Priors of the Crafts as the supreme magistrates of Florence. And, in the second place, they must attempt to bring the magnates effectively within the control of the laws and constitution of the mercantile community, which they systematically and recklessly defied as long as they were in a position to do so. The magnates behaved like brigands, and the people replied by practically making them outlaws. They gradually excluded them from all share of the government, they endeavoured to make the Podesta personally responsible for keeping them in order, they organized a militia of trade bands that could fly to arms and barricade the streets, or lay siege to the fortified houses of the magnates at a moment's notice; and finally, in 1293, they passed the celebrated "Ordinances of Justice" connected with the name of Giano della Bella, by which when a magnate murdered a popolano his whole clan was held directly responsible (the presumption being that the murder had been ordered in a family council), and "public report" vouched for by two witnesses was sufficient evidence for a conviction. It is this struggle for the supremacy of the mercantile democracy and the Roman Law over the military aristocracy with its "barbarian" traditions, that lies at the back of the Guelf and Ghibelline troubles of the thirteenth century. The papal and imperial principles that are usually associated with the names enter only in a very secondary way into the conflict. In truth neither the popes nor the emperors had any sympathy with the real objects of either party, though they were ready enough to seek their advantage in alliances with them. And in their turn the magnates and merchants of Florence were equally determined to be practically independent of Pope and Emperor alike. Nevertheless the magnates could look nowhere else than to the Emperor when they wanted material support or moral sanction for their claims to power; and it was only in the magnates that the Emperor in his turn could hope to find instruments or allies in his attempt to assert his power over the cities. In like manner the Pope, naturally jealous of a strong territorial power, encouraged and fostered the cities in their resistance to imperial pretensions, while he and the merchant bankers of Florence were indispensable to each other in the way of business.