In 1466 Piero sent Lorenzo, then eighteen years of age, to Rome on a mission of great moment both politically and commercially. Perhaps the most important part of the private business was to secure from the Pope a monopoly of working the alum mines discovered not many years before in the short range of volcanic hills lying round the little village of La Tolfa (Tofa), about eleven miles due west of Civita Vecchia and within the Pope’s dominions. A few deposits of alum had been known and partially worked in Europe, _i.e._ at Volterra and Ischia: but for all practical purposes almost all the alum used in Christendom came from Asia Minor, and the supply was always inferior to the increasing demand. A certain Giovanni di Castro prospecting among the hills round La Tolfa found what he believed to be an inexhaustible supply, “seven hills of alum.” Castro made sure of his find by calcinating the stone. He then hastened to Rome, appeared before the Pope, and somewhat grandiloquently announced his discovery. “I make known to you a victory over the Turk. He draws yearly from the Christians more than 300,000 pieces of gold, paid to him for the alum with which we dye wool of various colours, because none is found in Italy, save a little at Ischia.... I have found seven hills so abounding in alum that they might supply seven worlds. If you will send workmen, cause furnaces to be built and the stone to be calcined, you may furnish almost all Europe, and what money the Turk used to acquire will fall into your hands.” The Holy See made haste to secure the newly-found treasure, and in order to have a monopoly in the sale the Pope excommunicated every one who tried to import alum into Europe from the Turkish dominions. So determined were the Popes to maintain what in modern language would be called their “corner in alum,” that in the proclamation of Indulgences it was always expressly declared that the pardon promised did not include those who imported alum into Europe from the Turkish dominions. Such a deposit needed capital to work it properly and the Holy See farmed out the monopoly, protected by excommunication, to a firm of capitalists. Young Lorenzo was instructed to secure, and did obtain, this very valuable concession for his family. Hereafter the profits of the monopoly of alum were a source of great wealth to the Medici.