Again starting from Copernicus and letting the eye travel northwest along the Apennine mountains almost to the Caucasus, one arrives at a group of three beautiful craters which rest conspicuously on the level floor of Mare Imbrium. The largest of these craters is named _Archimedes_ after the most celebrated of ancient mathematicians. It is to be noted that lunar craters have been given the names of great men--Copernicus, Tycho, Kepler, great astronomers; Aristotle, Plato, great philosophers,--a very fine recognition of scholarly worth. Archimedes, 52 miles in diameter, has no interior mountain, but the shadows of its tall rim are imposing as they fall across its plain. [Figure 166: Some Interesting Craters on the Moon.] _Aristillus_ is about 34 miles in diameter, and 10,000 feet deep. In the center of this deep cavity rises a massive many-peaked mountain whose base is often lost in the darkness of the crater's shadows. _Autolycus_, south of Aristillus and somewhat smaller, is 23 miles in diameter with a floor somewhat depressed below the country which surrounds it. [Figure 167: Some interesting Craters on the Moon.] On the "shore-line" of Mare Imbrium, north of Archimedes, Aristillus and Autolycus, and not far from the "Valley of the Alps," lies _Plato_, one of the most easily found craters on the moon. Plato is a very huge oblong crater, 60 miles in diameter and containing an area of 2,700 miles. Its floor is exceptionally dark and flat and forms a striking contrast with the bright border of mountains which surround it. Quite a number of minute craterlets have been distinguished on its floor. The southern hemisphere of the moon, particularly as one approaches the region about the southern pole, is pitted with such a bewildering number of both large and small craters that astronomers say that it is relief to the eye to study the comparatively smooth, shaded portions of the globe after having gazed for any length of time at the crowded mass of detail in this wild and rugged region. The two craters in the southern hemisphere that are perhaps the easiest for the amateur to locate are _Clavius_, an enormous crater near the mountains at the southern pole, and _Tycho_, just below it, with its wonderful streaks, or rays. _Clavius_ is a crater of gorgeous depth and has an area of 16,500 miles. Around its walls and on its floor are many secondary craters, while from its center rise tall mountain peaks, one of which reaches 24,000 feet above the bottom of one of its included craters.