No Bathroom Wall out-lets or A/C!!??

[F2d5thCav]

@"Ninurta" 

Its symbol was d, from the Roman denarius.

... sez Wikipedia.

But that is odd, because Wiki goes on to say the denarius equaled 10 asses 

The word dēnārius is derived from the Latin dēnī "containing ten", as its value was originally of 10 assēs

so that still leaves the question as to why a coin associated with 10 of something came to be the source of an abbreviation for a coin associated with 12.

Cheers