At 103 meters long, 1.80 meters thick, and 37 meters high, The Roman Theater of Orange is a well-preserved theatre built in the 1st century AD for watching theatrical performances. It is still running today, which makes it the most memorable piece of architecture from the Roman Empire.
I think that the purpose of style for the Roman Empire was to flaunt wealth and status of the empire. Having lavish and grand trends in architecture made the empire come off stronger and superior to other empires.
The Notre-Dame is the most monumental piece of architecture from Medieval Europe due to its stand-out size and high importance, during the time. Cathedrals were very important, especially this grand one, because of religion was very important to medieval Europeans.
It's no question that Medieval European architecture was a sign and glorification of wealth. The execution of grand pieces of work, such as cathedrals, showcased the high values at that point in time--money, power, and religion.