What exactly were the Annunaki?

Giant hominoids, 8 feet tall, heavier, and more muscular than humans, visited Earth from their home planet, the Planet of the Crossing.

Niburu, Marduk, the Red Star, and recently Planet X are names for this planet. 

However, because the Sun and Earth's Moon were also numbered, the ancient Sumerians referred to it as the 12th Planet. 

According to the Zetas, there is life on the 12th Planet

The primary race in the Earth is a humanoid race 

Even now, the enormous hominoids of Planet 12 wear clothing reminiscent to Roman military garb

Rome in fact modeled after them, rather than these hominoids modeling after the Romans  

Unlike today's very muscular guys, the huge hominoids did not have abnormally large muscles

They have rounded muscles without the excessive bulging of muscle-men.