Cheek by jowl
Side by side; in close or intimate proximity
You might think that 'cheek by jowl' is a strange idiom to have been coined; after all our cheeks are always by our jowls. However, unlike the bizarre 'head over heels', this expression does actually make sense when we realise that it refers to our cheek being next to someone else's jowl, not to our own.
The expression 'cheek by jowl' is very old, in fact the earliest examples in print pre-date modern English, for instance, in Meredith Hanmer's translation of Eusebius of Caesarea, Socrates Scholasticus, and Evagrius Scholasticus - The auncient ecclesiasticall histories of the first six hundred yeares after Christ:
Cheeke by iole with the Emperour.
Soon after that, Shakespeare, always one to pick up on an ear-catching expression, used it in A Midsommer Nights Dreame, 1600, in which Demetrius says:
Follow? Nay, I'll go with thee, cheek by jowl.
This usage makes it clear that 'cheek by jowl' meant 'side by side'.