In place of the Iambus, a Tribrach ( v v v ) may stand in any foot but the last.
"New Latin Grammar" by Charles E. Bennett
His imagination is too bold to be confined by the petty limits of trochee or iambus.
"Continental Monthly, Vol I, Issue I, January 1862" by Various
As has already been said, the iambus is the common foot of English verse.
"English: Composition and Literature" by W. F. (William Franklin) Webster
It was not by chance that the line of five iambuses became the dominant metre of our language.
"Writings in the United Amateur, 1915-1922" by Howard Phillips Lovecraft
But others say that Torrhebus first used that mode, as Dionysius the Iambus relates.
"The Modes of Ancient Greek Music" by David Binning Monro