E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Serbonian Bog or Serbonis.
A mess from which there is no way of extricating oneself. The Serbonian bog was between Egypt and Palestine. Strabo calls it a lake, and says it was 200 stadia long, and 50 broad; Pliny makes it 150 miles in length. Hume says that whole armies have been lost therein. Typhon lay at the bottom of this bog, which was therefore called Typhons Breathing Hole. It received its name from Sebaket-Bardoil, a king of Jerusalem, who died there on his return from an expedition into Egypt.
Now, sir, I must say I know of no Serbonian bog deeper than a £5 rating would prove to be.B. Disraeli (Chance. of the Exch.), Times, March 19, 1867