Some scholars, such as Andrea Carandini believe in the historicity of Romulus. Why others doubt the historicity of characters with amazing deeds attributed to them with absolutely no shred of evidence that it's true, escapes me. I always thought the assumption was that such an individual existed be it Robin Hood, Jesus Christ, or even King Arthur himself.
As Plutarch notes:
Suddenly the sky was darkened, a thick cloud of storm and rain settled on the earth; the common people fled in affright, and were dispersed; and in this whirlwind Romulus disappeared, his body being never found either living or dead. A foul suspicion presently attached to the patricians, and rumors were current among the people as if that they, weary of kingly government, and exasperated of late by the imperious deportment of Romulus toward them, had plotted against his life and made him away, so that they might assume the authority and government into their own hands. This suspicion they sought to turn aside by decreeing divine honors to Romulus, as to one not dead, but translated to a higher condition. And Proculus, a man of note, took oath that he saw Romulus caught up into heaven in his arms and vestments, and heard him, as he ascended, cry out that they should hereafter style him by the name of Quirinus.
Romulus ascended bodily into heaven as the God Quirinus, joining Jupiter and Mars as part of the
All of this is absolutely true. We know because they found the cave.