The rooftops aren't called the Thieves' Highway for nothing
The Thieves' Highway is the slang term for the rooftops, mostly where they are in such a layout as to make a section of a city easy for thieves (and the likes) to move around unseen.
In Thief II, the roof tops of Dayport are referred to as a Thieves' highway which allow Garrett to move quite easily across the city to the Mechanist tower of Angelwatch without touching the ground.[1][2]
Notable areas referred to as a 'Thieves Highway'[]
- Dayport - Featured in Thief II Life of the Party.
- Old Quarter - Featured in Thief DS (Note, referred to as such in the Mobile version[3], and original version.[4]
- South Quarter - Featured in Thief DS (Not officially labelled as such, it is an area where a large shortcut can be made via the rooftops).