The inscription reads:

"M AGRIPPA L F COS TERTIVM FECIT"

Marcus Agrippa, son of Lucius, Consul for the third time, built this.

In fact, this Pantheon was built by Hadrian, as the brick stamps prove. Hadrian graciously gave credit to Marcus Agrippa who had built the previous Pantheon that had burned down in one of Rome's fires.
Pantheon

From:	Regina	(Wed 08 Oct 2003 07:52:52 PM EDT)
what does that say on top the building?