Messenger: What makes this woman think she can speak among men?
Queen Gorgo: Because only Spartan women give birth to real men.
The size of the Spartan's shield changes from the action battle sequences (smaller) to the scenes where they are more stationary, as well as, during the arrow attack (larger), presumably allowing greater mobility while fighting. This was confirmed in the Director's Commentary.
Some weapons used by 300 are actually weapons from previous war epics like "Alexander" and "Troy." They were used in this film to cut costs.