The antonyms for the phrase "arches over" could be "sinks under," "drops below," or "descends beneath." These words describe the opposite action of something rising or extending upwards, as opposed to arching over. Other possible antonyms could include "shrinks away," "recedes," or "withdraws," which suggest things moving backwards or retracting. Conversely, "reaches up," "surges forward," or "expands outward" could be antonyms that convey a sense of movement and growth, rather than collapse or contraction. Overall, antonyms for "arches over" might vary depending on the context and intended meaning of the phrase.