‘This city has a circular form, and such a marvellous roundness is the sign of its perfection. A trench of surprising beauty and breadth surrounds this city and contains, not a swamp or a putrid pool, but living water from fountains stocked with fish and crayfish.’ For friar Bonvesin de la Riva at the end of the thirteenth century, as for most of his successors, glorifying Milan consisted of singing the praises of its running water. Abundant, regular, gushing water was everywhere; it was ‘marvellous to drink, clear, healthy, within reach of the hand’.This praise is evidently for the geographical situation of Milan, which brought it harmony and wealth. But it is also for the Milanese themselves, who brought running water from the rivers to the Lombard capital. Milan, after all, was naturally ‘Medio-Amnium’, at an equal distance from the two rivers (the Ticino and the Adda) that flowed around it. At the end of the Middle Ages, it was at the centre of the most immense system of navigable rivers in Europe, and it owed this condition to three centuries of effort during which the communal power, but also private initiatives, had dug the canals and connected the streams. Water became the vital element in the economy, and the development of Milan multiplied the concurrent, sometimes rival uses of it. How could stagnant water from trenches be reconciled with that of the navigable rivers? How could it be ensured that the water that irrigated the garden would also supply the needs of the paper mill? There were many economic contradictions that could be resolved only by an equitable and measured sharing of the water. At the same time, the growing strength of the seigniorial and territorial state sought to appropriate the management of the water to itself. If the prince succeeded in guaranteeing a supply of clean water, which flowed constantly for the good of the whole community, he would have found the best way not only of participating in the development of his city but also of ensuring that his own power was retained.