Latifundia?

[Andy1984]

You can find the EB-building trees in your RTW/EB/documentation/JMRC Building trees.

For the Romans, you need several other structures before being able to build the latifundia.
- lightly romanized province (or higher)
- grant of land (ager divisus et disignatus): this is the scroll-like building that costs you some 5000 mnai, is built in a single turn which improves happiness by a mere 5% :D
- agricultura colonica (colonial farming): the second level of farming
- villae rusticae (agricultural estates)
- latifundia (industrialized agricultural estates). In order to build this specific building, you need to have at least a romanized province (lvl 2 government or higher), the small market (macellum) and a large city. The former buildings can be built in any minor city.

As a sidenote: you'll need to achieve several other conditions in order to trigger them. One of them includes reaching 172 BC. Also the FAQ states you should have more than six latifundiae in Italy, so you may be forced to build the seventh.

What they do? They give a law-penalty (-10%), a trade-bonus and I believe a bonus for demographic growth (+1% or +1.5%) as well.