What rocks are these?
Rashi: They are the same rocks mentioned above (4:8).
What is "Mishnas Toras Moshe" that they wrote on the rocks?
Radak: It is the essence of each Mitzvah. You cannot say that they wrote the entire Torah! It was "Be'er Heitev" (Devarim 27:8), i.e. in 70 languages.