As the Oxford English Dictionary explains it, the ancient Roman alphabet did not have a letter “w.”

So in the 7th century, when the Latin alphabet was first used in early Old English writing, it was necessary to invent a symbol to represent that sound.

At first, the sound was represented by “uu”—literally a double “u.”

It wasn’t written as a “v” because the letter “v” didn’t exist in Old English, as we’ve written before on the blog. And a double “v” would not have approximated the sound anyway.