Lunar craters

[Androcles]

http://www.jaxa.jp/press/2007/11/img/20071107_kaguya_02l.jpg
http://www.lpod.org/wp-content/uploads/2007/11/20071107_kaguya_LPOD.jpg
http://www3.nhk.or.jp/kaguya/archive/original/kaguya087.jpg

One has to notice that more recent impact craters are deeper relative to
their diameters than older craters, the larger of which appear to have
been back-filled.
For example, the crater wall of Pythagoras appears to have collapsed.
http://orbitalhub.com/wp-content/uploads/2008/10/kaguya-pythagoras-crater.jpg
If the Moon once had a crust and mantle like the Earth then an impact
could have broken right through the crust to leave a molten "floor"
to the crater which has long since solidified.