1648: Origin of ∞ Jun 19, 20109

The infinity symbol ∞ may appear to have been chosen as it loops, and therefore doesn't have an end, but this wouldn't be the full story. The first time it was published in math was 1655 by John Wallis, though it was used in Christian symbolism long before then. There are a number of theories as to why ∞ came to be, including that it looks like the Greek letter ω—the final letter in the alphabet—and that it looks like the Roman numeral for 1,000 (i.e. many), which is now thought of as an M, but in the medieval period was written curved almost like a sideways Theta θ, or even just CIƆ. In the former case, ω is used for certain sets in set-theory, and many cultures have used big numbers to signify 'countless' (like 'myriad') so both theories are sensible really.

See more about symbols of infinity here.