There was a graphic used for the Portuguese Wonder that I believed could be put to better use.
Through fortitude and endurance....
THE IMPERIAL PALACE WAS BORN.
The Imperial Palace is essentially a much more powerful version of the Castle with its own flame arrow attack and it produces four powerful and expensive Legendary Units.
The Imperial Palace costs 100 Wood, 100 Gold, and 1750 Stone. Incredibly expensive, incredibly powerful.
Picture is for size comparison. As you can see, the Town Center also has new units. In Empire Earth, the capacity for a Town Center to train Heroes was a last ditch defense utility.