During the greater part of the twelfth century, Pisa was in a permanent state of war with Lucca; but, though the chroniclers of both cities record the vicissitudes of the struggle, it is by no means easy to arrive at a definite opinion with regard to anything but the general results. The most inaccurate of modern historians is relatively at the mercy of his material; in the Middle Ages the material lay at the mercy of the chronicler. If, however, the details of the conflict are confused and doubtful, the conditions which produced it are fairly obvious. We have already seen how, during the Longobard and Frankish periods, the diocese of Lucca had been enlarged at the expense of the diocese of Pisa. The prolonged dissensions which resulted reproduce, in many of their essential features, the earlier and more celebrated dissensions between the Bishops of Siena and Arezzo; and even after questions of episcopal jurisdiction had developed into questions of communal sovereignty, the bishops did not abandon the contest. Indeed, the solidarity of their interests with those of their respective cities was so complete that, at first sight, it is difficult to discern whether the wars between Pisa and Lucca were, in fact, episcopal or communal wars.