The 6 gates are:
3 little gates:
1.Sarmi-Zeget-Usa,the Future Capital of the World
2.The Sphinx
3.The Cave of Zalmoxe

3 Great Gates:
1.The Round Clearing of Padis
2.The Avoided Hill where no living creature lives
3.The Happy Cemetery

And the 7th Gate is Atlantis ,the City itself
Once activated,ALL the Atlantean cities in this galaxy will activate