[Khubilai, "the great Khan"] has many concubines provided for his use, from a province of Tartary named Ungut, the inhabitants of which are distinguished for beauty of features and fairness of complexion. Every second year, or oftener, as it may happen to be his pleasure, the Great Khan sends thither his officers, who collect for him, one hundred, or more, of the handsomest of the young women, according to the estimation of beauty communicated to them in their instructions.Source: Marco Polo, Travels, in a modern edition based on the 1818 translation by Edward W. Marsden. This is, or was, the translation used by Everyman's Library and is thus perhaps the one most widely dispersed among English readers. I'm using a moderately spruced up 20th Century version edited with an introduction by one Manuel Komroff, first published by Liveright in 1926 The quoted passage is from pp 125-6 of a 1982 paperback version. Here's a genial review of a more recent reprint.
The mode of their appreciation is as follows. Upon the arrival of these commissioners, they give orders for assembling all the young women of the province, and appoint qualified persons to examine them, who, upon careful inspection of each of them separately, that is to say, of the hair, the countenance, the eyebrows, the mouth, the lips, and other features, as well as the symmetry of these with each other, estimates their value at sixteen, seventeen, eighteen, or twenty, or more carats, according to the greater or less degree of beauty. The number required by the Great Khan, at the rates, perhaps, of twenty or twenty-one carats, to which their commission was limited, is then selected from the rest, and they are conveyed to his court.
Upon their arrival in his presence, he causes a new examination to be made by a different set of inspectors, and from amongst them a further selection takes place, when thirty or forty are retained for his own chamber at a higher valuation. These are committed separately to the care of certain elderly ladies of the palace, whose duty it is to observe them attentively during the course of the night in order to ascertain that they have not any concealed imperfections, that they sleep tranquilly, do not snore, have sweet breath, and tare free from unpleasant scent in any part of the body. Having undergone this rigorous scrutiny, they are divided into parties of five, and each taking turn for three days and three nights, in his majesty's interior apartment, where they are to perform every service that is required of them, and he does with them as he likes. ...
Did Marco Polo ever actually go to China? The skeptical case is set forth here. Smarter and better informed people than I have no doubt that he did, but I join the skeptics. He didn't attempt to publish until years after the event, at a time when he needed the money (inter alia, he was in jail). He seems to pay a lot of attention to some things while simply ignoring seemingly important items just next door. My guess is that he went part way, and assembled a lot of traveler's tales.