Hagia Sophia is the first known example of this type of construction, which was a big technological advancement from previous church architecture. The dome, which is circular, is built on this base, which converts the weight of the dome onto the four corners, which coincidentally creates a square shape. Then, other walls or other half domes can be built under the arches and don't have to hold any of the dome weight.
If you don't know this yet, I'll be taking an art history class starting in January, and so I'm preparing myself by studying a little now. So far, this is my fave thing that I've seen.
Here is all I can show you of my day's work in actuality: failed Christmas card designs. These either didn't work the way I imagined them, or were just too plain boring and not cute. Well the bottom left one is not bad in regards to cuteness, but I'm still bored. I did finally come up with a design I love, which I of course am not showing here--that would ruin the surprise!
The other stuff I worked on today is part of Santa's elves' workshop. You'll see photos in January!