The dam divided the
river’s course into a lower, open, harbor and an
upper, closed one. Ship traffic and all the
flowing water were diverted by two new canals
on the left and right of the Amstel. Later, two
more moats were dug for defensive purposes
and fed by water from the Amstel.
Representations of the city reveal that the second half of the 16th century was engaged in
another extension of the fortifications. The old
moat around the walls was again changed, this
time into a shipping canal, which kept the name Singel (moat). A modern ring of fortifications
strengthened by bastions was meant to encircle the greatly enlarged harbor on the east side.