A rich nation, constantly embroiled in warfare and more often than not being invaded, has built, about a couple decades ago, a grand city over the old capital.
It houses a very large population of 300 thousand, and it's very well strategically placed, about 50 kilometers from the city lies the coast, with another, albeit much smaller, similarly built city acting as port, this is great because the ocean in which the coast is set brings very rich trade, which made both cities major trade hubs in the continent.
The city is built on top of fertile plains and has a particularly thick river running through town. The technology available to the civilization is similar to that of the late 16th century and early 17th, along with the architectural / engineering knowledge of the Romans (not sure if the Romans would be able to rival that of the 16th century Europeans in this aspect, but the Rome was the first city to achieve a population of one million in Europe [133 B.C.], a feat only seen in Europe again after nearly two millennia [London 1810 A.C.], and they had a pretty awesome sewage system, which I intend to mimic in the city).
As already mentioned, the nation is constantly warring, so the city has huge, thick walls, with many bastions around it, similar to the walls of star fortress, made to deflect cannon fire, allowing the city to hold besiegers at bay if their only hope of conquest is through an invasion on the city.
The city is also built to withstand a long siege, it has huge underground storehouses that store food and supplies, and I thought of having large farms and estates inside the city, but I think that it would take up too much valuable space and would not be cost-effective or efficient. I also thought of some sort of vertical farming mumbo jumbo but I'm not sure of how that would work.
The city is also a knowledge hub, it has three universities, four military schools, an observatory, many schools and it houses the central government, the royal palace and the court, and contributing more to the scholarship of the city, the community is, as already mentioned, an economic center, attracting merchants from all over the world, and many markets and banks have been built on the city, attracting even more traders.
Last but not least, I'm aware that the city would be VERY expensive to built, but that won't be a problem, for the kingdom has since long been wanting to build a grandiose capital, and has hoarded money / goods / resources for centuries to build such city, and even then that nearly wasn't enough, the government almost got in debt and lost a lot of influence because of the construction, but eventually, it paid off, so finances won't be much of a problem here fellows.
So, with this information in mind, how large would be this city? Keep in mind that it was also built with a small "extra space" to allow growth.
P.S. - I'm an architecture illiterate, so please explain your ideas to me, and point out my mistakes. P.S. 2 - If anyone has a cool sounding name for the city, I'm all ears.