Illud te, Tulle, moneo—I warn you, Tullus.
What is illud doing in this sentence? It doesn’t seem to be necessary.
Illud is a complement of moneo. “I admonish/warn you of this.” Moneo can take two accusative complements: (1) the person admonished/warned; and (2) the thing admonished/warned against, moneo aliquem aliquid. See Lewis and Short I(g) (this looks like a typo for I(c)):
http://perseus.uchicago.edu/cgi-bin/philologic/getobject.pl?c.11:2125.lewisandshort