@Pavía
#1
I think, that in Łęczyca (this smaller one in Łęczyca) should be Marsh/Wetlands as terrain. City of Łęczyca is next to Warsaw-Berlin glacial valley and between 2 rivers like Bzura and Ner (tributaries of the Vistula and Warta/Odra rivers). Due to wetlands, it was only dry passage in this place, where those wetland narrow to around 2-4 km, so it was used as one of amber routes few centuries earlier. I heard from locals histories, that City of Łęczyca was founded to make some money from traders on this amber route.
--> Currently, there are still wetlands and peat bogs near Łęczyca.
#2
Will be an event to build of a Castle in Łęczyca? Casimir III (the ruler of Poland) was famous for funding the construction of castles in Poland.
Casimir III ordered the construction of Castle to Władysław "the Hunchback" of Piast (current Duke of Łęczyca) about 1345. It can be related with increasing development in provice and giving some money for it, due to existensce of important Collegiate Church in Tum (village next to Łęczyca) built in the mid-12th century.
#3
Culture in Duchy of Łęczyca and Duchy of Sieradz isn't Lesser Poland or Greater Poland or Mazovian or even Silesian. It was kind of small and separate culture. This region was a kind of buffer between Greater Poland or Mazovian, like Kuyavian Culture is neither Greater Poland or Mazovian, it's something different.
Those regions in "Central Poland Area" could have named Cultures as Kuyavian, Łęczycan and Sieradzan. Maybe creating new very small culture isn't good idea, but i think it can be done like Sudovian and Curonian, where culture is mixed with neighbor. Or just mark this region as mixed culture not assigned to only one.
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I am from this region and want to help make the information and the game more historically accurate.