Didn’t he invade Dacia to raid their gold mines to finance the building of Trajan’s Forum, an eternal monument to himself?
No, but that was one of the things that was financed that way. The project (or some kind of project) had been begun by Domitian, but Trajan constructed a couple of large public markets, what most urban and suburban places in the US call ‘farmers markets’. We can’t know now, but these kinds of projects in ancient Rome probably served as urban renewal.