This is what I have found:
The Roman measure of length used for land was the actus of 120 feet: the square actus was 14,400 square feet; and a juger or jugerum was two actus quadrati. The word centuria properly means a hundred of any thing. The reason of the term centuria being applied to these divisions may be, that the plebeian centuries contained 100 actus, which is 50 jugera, the amount contained in the portions put up to sale by the quaestors: but Siculus Flaccus (p.15, ed. Goes.) gives a different account. The centuria sometimes contained 200 jugera, and in later periods 240 and 400. This division into centuriae only comprehended the cultivable land.The article is by one George Long, M.A., Fellow of Trinity College, and is found in
A Dictionary of Greek and Roman Antiquities, ed. William Smith, D.C.L., LL.D. (London: John Murray, 1875), pp. 29-31. I have excerpted from the website
http://www.ukans.edu/history/index/europe/
ancient_rome/E/Roman/Texts/secondary/SMIGRA*/Ager.html
Edit-in: I've split the link in half to stop the screen going WIDE. I could see it just fine on my screen, but apparently not all monitors do the same. Sorry if anyone's been going crazy with it. [sorry, sorry e]
