"You descend from the forest into the city."
Translation:De silva in urbem descenditis.
de - think, even if you don’t write it as such: ‘down from’.
That idea is already in the ‘de-scend’, so that would be too tautologous here, but perhaps not another time.
De also has the meaning: ‘about, concerning, relating to:’
De Bello Gallico - ‘(the Book) About the War in Gaul (= Gaulish War)’.
Redundancy like this is not a problem for Roman authors. A few examples include “de vita decedere” (Cicero), “de digito anulum detraho" (Cato), “de muro se deicere” (Plautus), among many others.
"De silva in urbem descendis" should be accepted...but so should "ex silva" and "ab silva."
According to Lewis & Short, dē signifies "the going out, departure, removal, or separating of an object from any fixed point. Accordingly, it occupies a middle place between ab, away from, which denotes a mere external departure, and ex, out of, which signifies from the interior of a thing. Hence verbs compounded with de are constr. not only with de, but quite as freq. with ab and ex; and, on the other hand, those compounded with ab and ex often have the terminus a quo indicated by de), from, away from, down from, out of, etc."