With the later versions of WordPress, whenever you add a tag to a post or a page and subsequently publish that post or page, the tag becomes part of a tag archive for that specific tag.

What happens when you later remove a post with a tag, or remove the tag, and the tag archive for that specific tag no longer exists because it was the only one? An HTTP 404 error is reported to any client requesting that URL.

I have decided to do something a little different. I have created this "tag graveyard" specifically for robots that refuse to quit looking for tags after they received 404 error codes multiple times (sometimes hundreds of times – bad robots). The tags that no longer exist will point to this page.

Perhaps, just perhaps, if the dumbest of the dumb robots get valid pages via 301 redirects, they'll stop looking over and over again for something that isn't here anymore. This is my tag graveyard, where WordPress tags come to die.