So, this is confirmed, the Starseed is what the symbol on the flagpoles represent.
Altough gbagok intepretation is awesome (I really love the idea of the 3 aligning planets!), the circle represent the seed, the "half moon" part is the energy radiating from the seed, when it created the universe during the Big Bang (as told in The Search)
The Starseed was used by the Overlords of the Eternal Dimension to create the universe and left to the Ancients.
It's very important as it ties lot of things together, including He-Ro's powers, Grayskull, and the 3 Towers.
The Central tower is a temple built by Ancients (with the help of their master architects, and Noah and Hordak were some of them) on top of a well leading to the chamber of the Starseed at the center of Eternia
I'm dropping more hints and let you guy start the guessing game again
So, we have the Starseed at the center of Eternia, but the well leading the the Central Tower is not the only passage to the surface.
There are at least 2 more. Based on all the existing info about MOTU, can you guess which they are?
Sounds like a silly question, but if you guess the answer right, you'll discover there is a lot more about it!
