Forum Romanum
Outlines of Roman History: Reformed Constitution
A description of organization of the Roman army, set up in the 6th century BC, by the Etruscan king, Servius Tullius. This was the basis of the army through the Republic.
Forum Romanum
Outlines of Roman History: Times of the Gracchi: Causes of Civil Strife
In a chapter from William Morey's 1901 textbook, he explains the make-up of the Roman populus at the beginning of the Late Republic.
University of Chicago
University of California: Mausoleum of Hadrian
This site from the University of California contains a brief section of information on the Mausoleum of Hadrian, also with pictures. Not too in-depth, but rather interesting to check out.