Rubicon

Rubicon, a famous river of Italy, associated with Julius Cæsar, now identified with the modern Fiumecino, a mountain torrent which springs out of the eastern flank of the Apennines and enters the Adriatic N. of Ariminum; marked the boundary line between Roman Italy and Cisalpine Gaul, a province administered by Cæsar; when he crossed it in 49 B.C. it was tantamount to a declaration of war against the Republic, hence the expression “to cross the Rubicon” is applied to the decisive step in any adventurous undertaking.

Definition taken from The Nuttall Encyclopædia, edited by the Reverend James Wood (1907)

Rubens, Peter Paul * Rubinstein, Anton
Rowton Heath
Roxburghshire
Royal Academy of Arts
Royal Society of Edinburgh, The
Royal Society of London
Royan
Royer-Collard, Pierre Paul
Royton
Ruabon
Rubens, Peter Paul
Rubicon
Rubinstein, Anton
Rubrics
Ruby
Rückert, Friedrich
Ruddiman, Thomas
Rudolf I.
Rudolf II.
Rudolf Lake
Rudra
Rugby

Nearby

Rubicon in Brewer’s Dictionary of Phrase & Fable

Links here from Chalmers

Caesar, Julius
Paine, Thomas