We bought our tickets to the Topkapi palace inside the first courtyard, and entered the second courtyard through an imposing gateway (featured photo) called Orta Kapi. This is Turkish for a very prosaic name: middle gate. The gate is as impressive as it looks here, with the two Byzantine-looking towers standing over it. The calligraphy on either side of the doorway is the ornate calligraphic seal (tughra) of sultan Mehmet II, who conquered Constantinople in 1452 CE and started building the Topkapi palace in 1459.
Topkapi is not a single palace, but a complex of palaces built over the next three centuries. I found it slow going, because it is so ornate that you pause to take in the details of various rooms and pavilions you pass through. Like most Islamic art, the colourful tiles, the beautiful geometric designs of inlaid wood or lattice work, and the variations on domes and arches, are what catch the eye. But here one can see a succession of building materials, and discoveries in geometry. One example was the use of a fivefold symmetry on some doors. It seemed to have been invented in the mid-17th century, and retro-fitted into several doors. The more common three, four, and six-fold symmetries can be seen everywhere.
I end with a view of the Bosphorus from the fourth courtyard of the palace. This was my first view of the doorway between the Mediterranean and Black seas, and between Europe and Asia. The overcast sky was very dramatic. As I took photos, the mournful bass hoots of ferries was counterpointed by the mewing of gulls as they flew over us. This must be the most memorable part of the soundscape of Istanbul.