City Hall and the Market Battery

One of the oldest images at the Archives is this Sheldon photograph of City Hall and the Market Battery from 1857. The clarity of the image is remarkable, and it was presumably taken from the Shoal Tower in what is now Confederation Basin. The Market Battery which is in evidence in the forefront was erected in 1848, prior to the construction of City Hall. Difficult to discern from this picture is the thickness of the walls. Rising 25 feet directly out of the water, the outer wall was wide enough to support a “horse and rig” upon its surface. The construction of this structure was credited to Briggs and Crawford, contractors.
The fortifications were constructed in the wake of the 1846 Oregon Crisis. City Hall was completed in 1844.
Any idea when they were removed and why?