smallpox - delay city creation

Hello!

One thing which came into my mind, when I  build
a new city on a field that was allready lined with a
railway: What a waste, the city will build it anyway...

So what makes building new cities so profitable is
the instant creation of:
- road (and railway)
- irrigation
- and a fortress
at now cost and without any delay.

Whereas you have to invest several turns to build
the same on a normal field. In addition: have to pay for
the upkeep of the settler during this time.
Why not let the building of a city require several
turns for building fortress, road and irrigation
(if available: and railway)

Like on normal fields this could be accelerated by
building with two or more settlers/engineers
or if the field allready has roads, irrigation or a fortress.

Maybe this could diminish the benefits of smallpox...

Horst