[Brown Deer]

Like I said...

It can't be "the", if like you said, it is one of many.

[Nero Germanicus]

Try looking at it this way, Great Britain has had many Kings and Queens. They are “historic,” even the current monarch.
It’s the same with the London Bridge(s).

his·tor·ic
histôrik,-stär-/
adjective
1. famous or important in history, or potentially so.
“we are standing on a historic site”

[chaosagent]

Right now it is ‘the’ because it’s ‘the’ only one.