There were scribbles all along the wall.
落書き + あった (= there were) is not a natural collocation in Japanese. It awkwardly sounds like “the scribbles EXISTED on the wall” in English. 落書き is not like a painting that someone draws on a canvas and hang it on a wall. But 落書き is an activity directly done on a wall. Here are more natural translations:
その壁は落書きだらけだった。= (lit.) The wall was filled with scribbles.
その壁は一面に落書きがされていた。= (lit.) The scribbles were drawn all over the wall.
落書きする or 落書きをする (to scribble) as a verb is a common expression.