Istanbul is the oldest city in Asia Minor, and one of the oldest cities in the world, having been continuously inhabited since 685 BC. Located on both the east and west sides of the Bosphorus Strait, Istanbul is the only metropolis to span two continents (Europe and Asia).
NASA has a pretty great picture of the Bosphorus that was taken from the International Space Station in 2004.
In the heart of the Thracian side of the city, nestled amongst church and mosque alike, lies a wonderful track. You can click on the image for a larger picture in which you can see all the religious buildings.
Just to the northwest of the track is a large wall running mostly north and south.
This is part of the Theodosian Wall, which was completed in 413 AD to keep out the likes of Attila the Hun, and stood until 1453 when it was breached by the Ottomans. You read right: that wall protected one of the most important cities in the world for over 1,000 years.