Bridge question

[Milky^]

1) Please explain, how can i make bridges, that are undestroyable, like in allied mission of YR, where objective was to defend London Parlament.
2)Is it possible to make one bridge straight over another?
_______---------------------_______ Second Hill.
_______|___-----------____|_______ First Hill
___________|________|____________ Nohill
[legend]
______land
-------bridge
| cliff
something like this, possibe or not?