Citybuildings.

[Lonecat Nekophrodite]

For the first day of playing Millennia. it is quite a learning curve how a city is founded.
First. There's no worker unit. improvements use different commands.
Second. city is more closely packing than Civ. While it is possible to build cities that's several tiles apart. border grows much slower.
Setters are made differently.
And Cities can only becomes fully functional (Region system replaced individual city. also Homeland means 'Capitol' in Civ sense).
How big could a city be in this game? While it is possilbe to determine fixed city distances in Civ 6. same rule doesn't apply here.

 

[Sephi]

Yes there is no hard limit to city size. It is really useful to leave space between your cities for later expansion.

 

[MrRadar]

Second. city is more closely packing than Civ. While it is possible to build cities that's several tiles apart. border grows much slower.

I'm not entirely sure of what do you mean here. But, just in case, space them out. And then space them out even more. I think, you want all the space inbetween your properly main cities as you can get. Those tiles are precious.

 

[Quintillus]

IMO, the lack of a worker unit is mostly an improvement. In some Civ games, half my time is moving workers around, and unless I'm playing India in Civ IV (who has faster workers), usually it's move to the tile one turn, perform the action the next. In Millennia, I just perform the action when I have enough infrastructure points to do so. The only problem is sometimes I forget that I have enough infrastructure points for some time, but I think there's an option to set a reminder for that?

City density has varied so much over the years in Civ. Civ VI tends towards widely spread-out cities, which ameliorates the downsides of Civ's 1 UPT combat (although I read an interesting article the other day arguing for dense city packing in Civ VI due to area-of-effect buildings). But look at the Infinite City Sprawl strategy in Civ III - it's far more densely packed than Millennia - and typical Civ III/IV cities are also more tightly packed than at least what I've built in Millennia.

I find it refreshing that Millennia does some things differently. Although, if you didn't enable the tutorial first, I would recommend it, it does a pretty good job IMO.