Some days later in a chance conversation with Marbois, Livingston spoke of his extraordinary interview with Talleyrand. Marbois intimated that he was not ignorant of the affair and invited Livingston to a further conversation. Although Monroe had already arrived in Paris and was now apprised of this sudden turn of affairs, Livingston went alone to the Treasury Office and there in conversation, which was prolonged until midnight, he fenced with Marbois over a fair price for Louisiana. The First Consul, said Marbois, demanded one hundred million francs. Livingston demurred at this huge sum. The United States did not want Louisiana but was willing to give ten million dollars for New Orleans and the Floridas. What would the United States give then? asked Marbois. Livingston replied that he would have to confer with Monroe. Finally Marbois suggested that if they would name sixty million francs, (less than $12,000,000) and assume claims which Americans had against the French Treasury for twenty million more, he would take the offer under advisement. Livingston would not commit himself, again insisting that he must consult Monroe.
So important did this interview seem to Livingston that he returned to his apartment and wrote a long report to Madison without waiting to confer with Monroe. It was three o'clock in the morning when he was done. "We shall do all we can to cheapen the purchase," he wrote, "but my present sentiment is that we shall buy."
History does not record what Monroe said when his colleague revealed these midnight secrets. But in the prolonged negotiations which followed Monroe, though ill, took his part, and in the end, on April 30, 1803, set his hand to the treaty which ceded Louisiana to the United States on the terms set by Marbois. In two conventions bearing the same date, the commissioners bound the United States to pay directly to France the sum of sixty million francs ($11,250,000) and to assume debts owed by France to American citizens, estimated at not more than twenty million francs ($3,750,000). Tradition says that after Marbois, Monroe, and Livingston had signed their names, Livingston remarked: "We have lived long, but this is the noblest work of our lives.... From this day the United States take their place among the powers of the first rank."