I personally think that concrete has been around longer than the Romans.
A reproduction of the sarcophagus lid of the Maya ruler of Palenque, King Pakal the Great, also known as K'inich Janaab' Pacal (23 March 603 CE - 31 March 683 CE). In this detail the king is falling into the terrible jaws of the Maya underworld, Xibalba.
Ancient alien theorists say it's a rocketship? What do you think?
