Is the "in" mandatory ? Couldn't it be an accusatif of direction like in "Romam ire" ?
I believe that only applies to cities and other words that take the locative (which is mostly cities, domus, and humus).
silva = forest = woods
Wouldn't a/ab work as well?
Descendere already implies a motion down, so "de" is a better preposition because is isn't just "from" but "down from". It's fairly common to repeat the preposition with verbs containing the same preposition as a prefix.
What word form is used with "de"?