It has been known since ancient times, and probably since prehistoric times. Remember that things like Mercury and Saturn, which are much harder to discern with the naked eye than the features of the moon, have been known since the beginning of civilization.

Plutach, the famous Roman author of the Lives, wrote a dialogue about the moon, "On the Apparent Face in the Orb of the Moon," which discusses the various features visible on the moons surface and argues that the moon is made of an earthen material rather than a mix of air and fire (as others had believed). If the moon were made of air and fire, how would the "face" on the moon remain constant? Plutarch's dialogue is remarkable because he discusses whether there might be life on the moon, but also because it contains this passage on why the moon does not fall to earth, in which a physical mechanism prescient of Newtonian gravity is posited:

there flows under the moon only thin air, not competent to support a solid body... And for this reason Pharnaces himself is under no apprehension of the earth’s falling, whereas he compassionates such as lie under the roadway of the moon, namely, the Ethiopians and people of Taprobane, lest so vast a weight should drop upon them; and yet, a safeguard to the moon against falling down is her motion, and the rapidity of her gyration, just as objects placed in slings have a hindrance from falling out in the circular whirling. For the natural tendency acts upon each object, unless it be diverted by some extraneous force. Consequently, her own weight does not act upon the moon, because by means of her rapid rotation its downward tendency is neutralized.

Kepler, writing much later (in 1608), described a journey to the moon and a discussion with its inhabitants. Kepler imagines how the earth would look from the moon. For those who live on the far side of the moon, they would never see the Earth at all, but those who live on the earth side would see it constantly, apparently floating in the same part of the sky and never rising or setting, just hanging motionlessly. Kepler's rhetorical conceit was to argue for heliocentrism by showing how complex a "lunacentric" astronomy would be (geocentric models are already very complicated, because the planets travel on epicycles which themselves travel in a circle around the sun. Lunacentric astronomy would add another layer of epicycles).

The first lunar map was made by Johannes Hevelius shortly after Kepler. This was made with the aid of the newfangled telescopes. It was thought at the time that people might be able to use the features of the moon to find exact longitudes during lunar eclipses (by timing when the earth's shadow fell on particular features). This did not prove practicable, though.