The Romans did not have a national flag as we think of today. In the very early days of the city, they had a flag that was flown on the Capitoline Hill to alert the people of an impending attack. It...
The Roman flag is the Italian flag which is a tricolor of red, green and white. There are various interpretations of the meanings of those colors as there are of any other flag's colors.
Flags were not in use for nations during the time of the ancient Romans. The only flags used were the military flags used by the cavalry and sometimes by the infantry for parade purposes.