The tide of Saracen invasion was met at Caorle and rolled back, and two great ships of war were constructed to guard the _porti_. Amid the stress of war the arts of diplomacy were not neglected. A treaty still exists, dated 840, between Lothair, “by Divine Providence Imperator Augustus and the most glorious Duke of the Venetians,” for a period of five years: their relations in peace and war are defined; mutual restitution of runaway slaves is promised, and traffic in the subjects of the contracting powers prohibited; the inviolability of ambassadors and of correspondence assured. Pietro had the honour of welcoming the first royal tourists (855) in the person of King Louis II. of Italy and his consort, who spent three days at Venice. The defeated Participazi were, however, biding their time. In 864 the people’s Doge was assassinated when leaving the Church of S. Zaccaria after Vespers and his body lay on the ground until nightfall, when the pious nuns gave it sepulture in the atrium of their church. The chroniclers record the great wisdom and piety of Orso Participazio, who succeeded the murdered Doge. He cleared the seas of pirates, and sought, by calling a synod of clergy and laity, to purge Venice from the iniquitous traffic in slaves, which continued to stain her commerce. Rialto was made healthier by drainage and building; Dorsodura peopled. The growth of the arts of peace may be measured by the fact that the Venetians were able at this time to make a present of twelve bells to the Greek Emperor. Orso died full of years and honours in 881, and was buried in S. Zaccaria. During the short reign of his son Giovanni a descent was made on Comacchio, a city on the mainland north of Ravenna, whose growing power and commerce roused the jealousy of Venice. The Venetians had long memories, and the help given to Pepin was now avenged by the devastation of the city and the country even up to the walls of Ravenna. In 887 Pietro Candiano, a devout Christian, and a wise and brave prince, was elected, and after a reign of five months met a soldier’s death fighting against the pirates. Pietro Tribuno, who succeeded him, was called upon to face a new danger. In the spring of 900 the Hungarians came down the usual track of the barbarian invaders by the Fruilian passes--“that most baneful gate left open by nature for the chastisement of the sins of Italy”--and ravaged the land. They were held too cheaply by Berengarius, King of Italy, and flushed with victory, spread terror even to the lagoons. The preparations made to resist Pepin were renewed. Rialto was fortified and a castle built on the island of Olivolo, which is called Castello to this day. By the way of the Franks the terrible barbarians overran the outer cities of the _dogado_, and made for the _Porto_ of Albiola. The Venetian fleet met them, happy omen, at the very spot where Pepin’s might was crushed. A fierce fight ensued, and the battle was again to the islanders.