Subject-auxiliary inversion after SO + adverb / adjective and SUCH
When adverbial or adjectival phrases starting with so are placed at the beginning of the sentence for emphatic effect, the subject and auxiliary are inverted:
So quickly did he run that the others couldn't catch up with him. (He ran so quickly that the others couldn't catch up with him.)
So strong was the wind that we couldn't open the window. (The wind was so strong that we couldn't open the window.)
So + adjective can be replaced with such:
Such was the wind that we couldn't open the window. (The wind was such that we couldn't open the window.)