A close examination of the photographs taken by American Rangers and by the Russian Lunik and Zond yields good arguments to assume a volcanic origin of large and medium sized lunar craters which are situated predominantly on the so-called "lands". On the other hand it seems likely that the multitude of small craters scattered uniformly over the entire lunar surface including the so-called "seas" are due to impacts of meteorites. Analogous morphological characteristics were revealed by NASA's Mariner IV of the surface of Mars. Consequently, the martian craters seem to have analogous origins. Peculiar and interesting is the remarkable resemblance of a group of these craters with the eruptive center of the "Colli Albani" near Rome.