downtown?

On the way into Tulsa this afternoon:

Nathanael: "Mom, downtown Tulsa is a LOOONNGG ways away." (He could see downtown from where we were.)

me: "Honey, it's not that far away."

Nathanael: "Mom, why is it called downtown? It must be down or something."

me: "uh, ummm, uh, well, I'm not really sure, I think that Tulsa started there and then grew out, uh, umm...We'll have to look it up." (typical "teacher-who-doesn't-know-the-answer" answer)

Nathanael: "Oh, well then we must be up....uptown or something."

me: scratching my head, smiling, and wondering how many more times I will be completely stumped by the questions of my small children. If anyone has any ideas or actually knows how the whole "downtown" thing started, I'd love to hear it so I can tell my 5-year-old!