When the Longobards became masters of nearly the whole of Italy, and subjected it to their long and cruel sway, they are known to have appointed a duke to every one of the principal cities they occupied. Rome remained free from them, having a Pope; Ravenna also escaped because an Exarch was soon to hold rule there, and almost all the cities by the sea were likewise exempted, inasmuch as the Longobards were ignorant of navigation, and needed assistance for their maritime trade. It was for the same reason that republics such as Venice, Amalfi, Pisa, Naples, and Gaeta, were of earlier origin than the rest. The dukes enjoyed great authority and independence; indeed, some of the duchies, especially on the borders, became so extended as to resemble small kingdoms--_e.g._, the dukedoms of Friuli, Spoleto, and Benevento. This circumstance greatly contributed to the decomposition of the kingdom and to the fall of the Longobards, whose strength and daring were never conjoined with any real political capacity. On the arrival of the Franks, counts took the place of dukes, but with less power and smaller territories. Charlemagne, with his genuine talent for statesmanship, refused to maintain lords who, in seeking their own independence, might endanger the existence of his empire. Nevertheless, as it was indispensable to keep his borders more strongly defended, he constituted _marches_, on the pattern of the greater Longobard duchies, and entrusted them to margraves, or marquises (_Mark-grafen_--frontier counts, marquises, or margraves). Thus too the marquisate of Tuscany was formed and the government centred in Lucca; for this city having had a duke of its own ever since the times of the Longobards, was already of considerable importance, while, as we have seen, Florence had fallen so low that the documents of the period merely refer to it as a suburb of Fiesole. Nearly all the margraves acquired great power, and aspired to still higher dignities. From their ranks in fact came men such as Hardouin and Berengarius, who, aspiring to form an Italian kingdom, became formidable opponents of the Empire, often wrought it much harm, and involved it in sanguinary wars.