As the other commenter pointed out, the distinction is that citizens of CCAA were citizens of Rome. You're right that Cologne was founded before "colonia" gaine

As the other commenter pointed out, the distinction is that citizens of CCAA were citizens of Rome. You're right that Cologne was founded before "colonia" gained its distinctive meaning of status, though, but my statement about Cologne having had that special status (especially compared to e.g. Mainz) is still true nevertheless. Of course you're also right that modern-day Cologne is bigger than just the Roman center but that's a bit pedantic. The Roman center is of course full of actual ruins (sometimes with medieval ruins on top of them) but artifacts in general (e.g. coins) are still discovered anywhere in the vicinity and especially along the historic roads. In the Roman city center it's enough of a problem that construction projects tend to be delayed extensively but even outside of it "Roman stuff" is still among the things you might accidentally find by digging, alongside more exciting things like live bombs from WW2 air raids. EDIT: It's also worth mentioning that there was also a military outpost on the other side of the river in what is now the "Deutz" district.