Apple Mail and massive "Archive" I can't get rid of

OK - so at some point with a beta in the last few cycles (I am NO LONGER running a beta OS), a folder labeled "Archive" showed up in Mail.app. This folder "box" contains a sub folder for each email account I have set up (7 of them).

If I individually click on each one, I get the following totals:

Acct. 1: 0

Acct. 2: 7

Acct. 3: 0

Acct. 4: 183

Acct. 5: 96,845

Acct. 6: 0

Acct. 7: 0

I have no rules set up to establish such an "archive", and I don't understand what the purpose is. If I delete an email listed in one of the above - it disappears, then reappears...

If it makes a difference - Account 1, 2, 4, & 5 are all "gmail" accounts...

Help please! There are emails going back over 5 years! There is no rhyme or reason to the emails there - it does not appear to have any full-blown "spam" identified messages saved - but does have everything from restaurant mass emails to stuff I actually might have saved in another folder that I keep for stuff like receipts. But again - these emails never actually delete! I can't get rid of them, and the database on my MacBook Pro is getting rather large!