Arcadia is a harsh world and sooner or later realms come under attack. Having an army is a priority to survive, while having a strong fleet will enable the realm to expand its influence across the seas.
In order to train ground units the city must have a Castle. Upgrading the Castle enables more training slots (maximum of 5) to increase the number of units that can be trained simultaneously. Units are trained in the city "Castle" tab by inserting the desired number of units and clicking "train". The training time and cost is given by multiplicating the time and cost of a single unit by the quantity to be trained (rounded upwards).
The resources required for training ground units are Lumber, Iron, Gold and male citizens, however for special units (Mages and Silver Knights) Diamond and Palladium may be required.
To get access to the training of more sophisticated units, not only the Castle but also other buildings must be upgraded (Swordmasters Guild, Archery Grounds etc...). The requirements for each unit can be found in the units list.
In order to build ships the city must have a Port (must be close to a tile with water) and the Shipyard must be built. Upgrading the Shipyard enables more training slots. Ships are built in the city "Shipyard" tab by typing the desired number and clicking "build". The building time and cost is given by multiplicating the time and cost of a single ship by the amount to be trained (rounded upwards).
The resources required to build ships are Lumber, Iron, Gold and male citizens.
To acquire the technology to build more advanced ships the Shipyard must be upgraded (along with the Blacksmith).