I founds this very useful and interesting site (https://www.reed.edu/ara-pacis/) while I was looking for information about Augustus’ “Horologium” . My interest was prompted by the discussion of “scrup.” (scrupulus) here http://discourse.textkit.com/t/copernicus-translation-help-needed/18209/1
It has many diagrams and pictures relating to the Augustan monuments of the northern Campus Martius.
I can also recommend this article which I can send to anyone who is interested and doesn’t have access.
Peter Heslin, Augustus, Domitian and the So-Called Horologium Augusti, The Journal of Roman Studies , 2007, Vol. 97 (2007), pp. 1-20.
There is quite a lot of misleading information around about the “Horologium” so it is useful to have this overview.