This 'gate' was originally constructed in the late 4th century far outside the Constantinian walls by Theodosius to acta as a triumphal arch on approach to the city. Theodosius II had a new set of walls constructed (the currently visible ones) and the arch was incorporated as a gate, remaining the triumphal entrance to the city thereafter. Sadly, much fo the arch was blocked to turn it into a fortified gate. It is now within the complex of the Yedikule fortress. The gate is usually sealed with a grill, though one of the custodians will usually let you through for a small gratuity. Outside the gate is much more visible. Also, the outer gate, known as the 'Little Golden Gate' is then accessible. Despite its bricking up and inclusion within a fortress, it is very easy to get an idea of the massive scale of the arch. The fortress that surrounds it is also interesting.

Access: Reachable by train or bus and attached to the city's walls, the Yedikule fortress is well known and anyone can give you directions. It is open 9:30 to 4:30 daily.

The land walls of Theodosius are probably the largest and most impressive non-religious monument in Istanbul. They completely seal off the land approach to the city, and with the sea walls, they completely enclose it. Much of the circuit has been reconstructed, and it is nice to be able to walk past ruined and reconstructed sections after each other. It gives a good idea of the walls. The reconstruction is a subject of much debate. Some serious historians have expressed admiration for the project and how it has been carried out, while others have been appalled by the work. I personally like the work, though I hope the entire length does not suffer it, as it would be a shame to lose the ruined original completely. These 5th century walls are remembered as the strongest city walls in the world. In addition to the great wall with its towers and gates and wall walk, there were additional defences. Outside this was a wide platform and then a second, smaller wall with its own parapet and towers. Beyond this was a wide moat. The defences held for many centuries until the advent of the cannon in siege warfare.

Access: The entire length of the land walls is walkable.

Sadly neglected and lost in the suburbs lies one of the few ruined Byzantine churches of Istanbul and certainly its best preserved one. This 5th century monastery suffered badly during the Crusader invasion of the city and was then destroyed once more during the Ottoman invasion. The church of the monastery was converted into a mosque and survived as such until the 19th century, since which it has been a ruinous shell.

Access: Hard to find, though close to one of the main roads and a railway station, the monastery was solidly locked up when I visited in 2008 and was only partially viewable from the outside.