Also, this may just be my eyes playing tricks, but if you trace the rectangle formed by the bottom opening and the fancy detailing above the arch, it looks to be a Golden Rectangle.
By the way, I actually do have CS5 now, I had to get it for some of my design classes last fall. Yay me :-). It never occured to me to use the vanishing perspective feature., however. Thanks for that tip.
I knocked up a little model in Silo...just for some practice.
Something else intirely, but i always have to say this, when i see a castle like this: the way to the castle is not put clever. Attackers marching at the castle are showing their left side to the castle, which is the side for the shield. One should always try to build a castle so that attackers would show their right side to the castle. This way they either march sideways (disrupting order in their ranks) or archers in the castle can hit their vulnerable right side, which is not protected by the shield.
In theory, perhaps. In practice, an approach to any determined defending castle is fraught with danger regardless of whatever side one bears one's shield. Shields aren't very good at protecting someone against projectiles lobbed from the top of high walls. Attackers will not even come within bowshot until defences have been breached, and depending on the aggressor's commander, that may or may not be directed at the gate. Sieges, historically speaking, tend to last only as long as it takes for one side or the other to run out of money, health or time. This can end with the garrison commander surrendering under terms, or the aggressors quitting the field. A formation of troops 'marching onto the castle' is generally a very good way of getting them all killed unless the castle is compromised, or their defenders are broken. So, you tend to keep soldiers out of the way until you know for sure they are going to make a lick of difference.
Siege warfare. Good times.
Edit: As an aside, and depending on the topography of the landscape the castle is perched upon, I'd be investing in breaching the wall on the east-side of the first gate house, but that depends if I have the money to spend on sappers, engineers or a couple of reliable canons. If I just had troops, and the money to keep them happy long enough, I'd just sit on them and wait for them to run themselves out of food, water and hygiene.
On magic, yes it changes things, but it takes a good deal of contrivance with a more than low-magic setting to have castles make sense, at least without substantial redesign. Even without spells, flying cavalry (winged horse, gryphons, hippogriffs, etc.) and fast-tunneling and wall-crawling creatures, castle walls become less secure. Walled towns still make sense for defense against bandits lacking magic and land animals.
Even in a high-magic setting, though, magic on that kind of scale is likely to be expensive. Probably most magical threats to the fortress could be neutralized by whoever lives in that wizard's tower. If magic is common and powerful enough to obsolete castles, then nobody will undergo the effort and expense of building them. Ergo, if this castle exists, it is not in great danger of being overrun by magical beasties.
Then again, magic of that kind would make large buildings easier to construct, if the wizards could be enticed into doing that sort of low work.