6.63 at beginning of clause: inversion of subject and verb

If you put a prepositional phrase which refers to the position of something at the beginning of the clause when you are using a verb intransitively, the normal word order after it is often changed, and the verb placed before the subject.

If you are using 'be' as a main verb, or a modal, the verb always comes before the subject; so for example, you cannot say 'Under her chin a colossal brooch was'.