It is a fixed and rather bookish expression. It originated from tradition, a translation method to read Chinese text word-by-word in Japanese. Japanese needs all elements before the main verb, but Chinese put some adjuncts) after the verb and the object, like English. In this case, it is customary to parse it as if the verb is an outer subject to the adjunct.
> "as protracted as a thread" →
> "be a follower for three years" →
> "you are handsome, very much" →
This becomes a fixed pattern to focus on the adverbial element, emphasizing how much the degree or amount is, not limited to numbers.
> "deeply I was grateful"
> "more than ever it is reassuring"
> "countless times one owes to somebody"
> "a half day of hard struggle"
Note that the style itself is a part of idiom, so no particle follows .