Ever since the Saxon settlers arrived in the early 12th century, invading Mongols, Turks and others gave them a tough time, repeatedly destroying the old settlements of Bartholoma and Corona. When they had quite enough of it all, the Saxons set themselves to build fortifications around their town, first consisting of earthen walls and wooden barriers, later reinforced with stones. Most work was done between 1400 and 1650, when outer and inner walls were erected, together with massive defence towers and gates.
The best place to start a tour of fortifications is on the northern side, at Strada Dupa Ziduri (which translates as Street Behind the Walls). You will find it just north of the Livada Postei bus stop, to the right (face on) of the taxi rank. The street starts out inauspiciously - as a car park - but soon gives way to a relatively nice walk alongside the old, high city walls. You will pass under the Bastionul Graft, a wonderful 15th century relic, well preserved and housing the usual museum of medieval weaponry and suchlike. Above it is the White Tower (Turnul Alb), which you can climb up to via some very steep steps – do not try it unless you are feeling extremely fit and agile. There are more steps when you actually get to the tower, but the views from the top are fantastic.
Follow the path between the wall and the canal (yes, it is a canal) a little further and you will see an old blue sign pointing the way to the Black Tower (Turnul Negru). You will notice immediately that the tower (which you can see by glancing up to your right) is in fact white. A steep path (but no steps!) leads up to it. The deck in front of it is a great location for photos. (The White Tower is open 09:00 - 17:00. Closed Mon. The Black Tower is closed during Summer).