Crispus. A.D. 317-326. AE3 (19mm, 3.71g). 

CRISPVS NOB CAS, Laureate and cuirassed bust left, holding spear and 
shield.
VIRTVS AVGG, Campgate with closed doors, three turrets above. 
P-R across fields.
Mintmark RP. 

RIC 180 var. Rome, A.D. 318-319 Obverse legend error. 
The impressive artistry of early Rome Mint campgates makes this 
coin a work of numismatic and architectural art. The archway of 
the "gate" has a 3-D perspective as do the portals of the turrets 
or what would more accurately be called watchtowers in my opinion. 

 Price 
  US$ 795.00   € 597.73
 £ 506.44
 AUD$ 802.56
 CHF 775.91
 CAD$ 801.36
 
Rates for 11/12/2010 
CRS36

Courtesy of imperialcoins.com, Nov. 2010.