The Collaborative International Dictionary of English v.0.48:

Sesterce \Ses"terce\, n. [L. sestertius (sc. nummus), fr.
   sestertius two and a half; semis half + tertius third: cf. F.
   sesterce.] (Rom. Antiq.)
   A Roman coin or denomination of money, in value the fourth
   part of a denarius, and originally containing two asses and a
   half, afterward four asses, -- equal to about two pence
   sterling, or four cents.
   [1913 Webster]

   Note: The sestertium was equivalent to one thousand
         sesterces, equal to [pounds]8 17s 1d. sterling, or
         about $43 (in 1900), before the reign of Augustus.
         After his reign its value was about [pounds]7 16s. 3d.
         sterling. The sesterce was originally coined only in
         silver, but later both in silver and brass.
         [1913 Webster]