Saint Seiya is the story of Athena's saints. The story focuses mainly on Seiya, Yoga, Shiryu, Shun and Ikki, 5 bronce saints whom in order to protect there ideals, they will fight even the gods.
The original story consists of 3 parts:
The Sanctuary, which tells the beggining of the fights of the saints due to the internal strife between Athena's saints.
The Poseidon arc, which tells the fight of the saints against the forces of the awakening Poseidon who is trying to flood the world.
The Hades chapter, which tells of the final holy war Hades wages against Athena in his attempt to throw the world into eternal darkness.
Furthermore, the serie continues in a new manga subtitled "Next Dimension", which is currently in serialization.
Just like DBZ, Saint Seiya power is a very controversial subject, some wanking it to saying it casually reaches quintillions of times lightspeed, others downplaying it due to some extremely inconsistant feats. However, Saint Seiya in reality is a very strong verse, beings that can create an earthquake with a finger are simple low tiers. This verse is filled with planetary threats, posseses multitude's of star system to galaxy busters, fighters capable of reaching FTL speeds and has a large amount of hax. Top tiers of the verse hang around universe level and are easily MFTL. Furthermore, the god tier of the verse, Chronos, is the personification of time and is at the very least universe+. Saint Seiya is one of the strongest verses in anime/manga, standing above verses like DBZ and even above verses like Bastard!!.