When an engineer has to construct a railway up a hill having a still steeper slope, he must secure practicable gradients by laying out the line in ascending spirals, if necessary tunnelling into the hill, as on the St Gothard railway, or in a series of zigzags, or he must resort to a rack or a cable railway.
In general it is not curvature, but change of curvature, that presents difficulty in the laying-out of a line.
The place was without importance until 1612, when Shah Abbas began building and laying out the palaces and gardens in the neighbourhood now collectively known as Bagh i Shah (the garden of the shah).
He was born in Abana, near the Black Sea, where his father was a bridge-keeper and his mother followed the despised profession of laying out the dead.
He, among others, prepared designs for laying out the City anew.
