AD 610-641. 32mm. Heraclius and H. Constantine standing facing /
     Large M, Constantinople mint. SB 810. Crude Fine. 
Overstruck on an earlier follis.

Courtesy of Stoa Image Gallery, album 131, Nov. 2010

Constantinople, mint-mark CON. This a very common yet very 
interesting type, celebrating the recapture of Jerusalem 
from the Persians and commencing a failed attempt at 
monetary reform.  

Heraclius is holding a long cross, whilst his son is carrying a cross on globe. It often looks like a long cross, 
but what can look like the shaft is actually the fold of his 
cloak.

See
(http://www.wegm.com/coins/heraclius.htm), 

"This class of follis was introduced in year twenty (629-
630) and represented a serious effort to return the copper 
coinage to its weight and value, at the beginning of the 
reign. The effort lasted until year 21, after which the weight fell from 9-11g. to 6-8g. From year 23 until the 
class was retired in year 30, the weight was reduced even 
further to approximately 4.5-6g.

Martina was dropped from these coins, presumably to give 
greater prominence to Heraclius Constantine. The C beneath 
the + above the denominational mark likely represents 
(Heraclius) Constantine. The emperor himself being depicted 
in military attire is a presumed reference to his recent 
victories of the Persians, while the long cross he is 
holding is representative of the True Cross his campaign 
restored. These are frequently overstruck on earlier coins, 
often of Heraclius' own reign."