known to human promises. I will not leave you until I have obtained
such a pledge of your constancy, which is necessary to relieve my
anxiety, and essential to my repose."

Ninon vainly argued that this would be something too strange and
novel, foolish, in fact, the Marquis was obstinate and finally
overcame her remonstrances. She wrote and signed a written pledge
such as no woman had ever executed, and fortified with this pledge,
the Marquis hastened to respond to the call of duty.

Two days had scarcely elapsed before Ninon was besieged by one of the
most dangerous men of her acquaintance. Skilled in the art of love, he
had often pressed his suit, but Ninon had other engagements and would
not listen to him. But now, his rival being out of the field, he
resumed his entreaties and increased his ardor. He was a man to
inspire love, but Ninon resisted, though his pleading touched her
heart. Her eyes at last betrayed her love and she was vanquished
before she realized the outcome of the struggle.

What was the astonishment of the conqueror, who was enjoying the
fruits of his victory, to hear Ninon exclaim in a breathless voice,
repeating it three times: "Ah! Ah! le bon billet qu'a la Châtre!" (Oh,
the fine bond that la Châtre has.)

Pressed for an explanation of the enigma, Ninon told him the whole
story, which was too good to keep secret, and soon the "billet de la
Châtre" became, in the mouth of everybody, a saying applied to things
upon which it is not wise to rely. Voltaire, to preserve so charming
an incident, has embalmed it in his comedy of la Prude, act I, scene
III. Ninon merely followed the rule established by Madame de Sévigné: