In these great disasters the inhabitants are afforded an opportunity of exhibiting their valour, and it is always the most energetic who succeed in protecting their property from being washed away by the floods. During the flood just referred {212} to, the inhabitants of the little town of Ostiglia fought successfully with the rising waters, whilst many of their neighbours succumbed. The town stands close to the _froldo_, and there is no second line of dykes to protect it. The dyke threatened to give way. The inhabitants at once set about throwing up a second barrier. All the able-bodied men of the place, 4,000 in number, turned out to work, headed by their mayor. They worked day and night, and, as the floods carried away the old dyke, the new one rose in its rear. The victory was won; the floods retired, and their houses were safe. Some of those breaches in the dykes have led to permanent changes in the course of the river, and these divagations have been most considerable in the delta. During the time of the Romans, and up to the thirteenth century, the Po di Volano was the principal branch of the river, whilst now it has dwindled down to an insignificant ditch which can hardly be traced through the swamps of Comacchio. Two other branches, farther to the south, are used now as carriage roads. In the eighth century the Po di Primaro, which enters the sea to the north of Ravenna, took the place of these old channels. Another bifurcation ensued in 1152, when the embankment at Ficcarolo was destroyed, it is said, by the people living above that town, and the main channel of the river, the Maestra, deserted the walls of Ferrara in the midst of its swamps, and united itself with the channels of the Adige. Breaches in the embankments usually take place in October or November, and generally at the same places. The danger is always greatest at Corbola, where the Po di Maestra bifurcates. The Adige is quite as great a wanderer as the Po. Scarcely has that river left its defile, or _chiusa_, of calcareous mountains and the fortifications of Verona than it begins its erratic course over the plain. In the time of the Romans the Adige flowed much farther to the north, along the foot of the Euganean Hills, and entered the sea at Brondolo. In 587 the river broke through its embankments, and its main branch took the direction which it maintains up to the present day, entering the sea at Fossone. But new channels opened repeatedly towards the south, until the Adige and Po conjointly formed but one delta. The Polesina of Rovigo, between the two rivers, and that of Ferrara, are low tracts of alluvial land. The courtyard of the Castle of Ferrara, which occupies one of the most elevated sites in these plains, is nine feet lower than the highest level of the Po when flooded.