they had fortified with castles, and after the army had crossed, destroyed them. Then we dismantled three of their fortresses ... and after we had celebrated Christmas with great merriment, we marched by way of Vercelli and Turin to the Po; we crossed the river and destroyed the strong city of Chieri, and burned Asti. This done, we laid siege to Tortona, most strongly fortified both by art and nature; and on the third day, having captured the suburbs, we should easily have carried the citadel, if night and stormy weather had not prevented us. At last, after many assaults, many killed, and a piteous slaughter of citizens, we forced the citadel to surrender, not without losing a number of our men."[10] Such vigour as this reduced Milan and her sister cities to obedience. But Frederick was not content with raids into Italy and spasmodic punishment administered to this rebellious city or to that; he wished to have the Imperial rights and authority definitely settled on a permanent basis; so he convoked a diet on the plain of Roncaglia, not far from Piacenza, to which he summoned bishops, dukes, marquesses, counts, and other nobles of the realm, four famous jurists from Bologna, and two representatives from each of fourteen Lombard cities. Frederick was a just man; he merely wished his legal rights, and proposed to ascertain what those rights were. The determination was left to the lawyers. By this time lawyers had already begun to play a part in public affairs. Roman law had never been lost. For centuries it had remained side by side with the customs of the conquering Barbarians, less as a code of laws than as the tradition of the subject Latin people; and, when the needs of quickening civilization required a more elaborate system of law than custom could supply, there was the Roman law ready for use. It suddenly leaped into general interest, and rivalled the Church as a career for young men. St. Bernard complained that the law of Justinian was ousting the law of God. In 1088 the great law school of Bologna had been founded. Thither students crowded by thousands; and the opinions of its jurists were received with the deepest respect.