
On the far right of the oil painting by William Marlow (1740 -1813) you can see a huge mound, this was the site of the Worcester castle and motte.
It was built in 1069. It stopped being a defensive building in the 13th century. It was quite a large motte (judging by the painting) and would have been a good defensive point for the earliest settlement of Worcester. The Diglis area is, I believe, the oldest part of Worcester.
The Castle was used as a prison until 1814.
Perhaps the blocks were part of that prison, however, the motte wasn't dismantled until between 1823 - 1846, it would have had to been excavated first leaving the outer wall / walls in place.
I'm not sure that the City walls came that far South or crossed Frog brook at that point, I do know that Frog brook was diverted when the canal was built and that the walls crossed Frog brook at Sidbury.
What is known is that the original Worcester Castle stood at that spot and the walls, or most of them, were eventually used to rebuild the City walls.
I wonder if the Worcester archeologist's department did a dig there before Taylor Wimpey built their apartments?