Why we're the twelve tables created?

That is easy  the Twelve Tables (aka Law of the Twelve Tables) was a set of laws inscribed on 12 bronze tablets created in ancient Rome in 451 and 450 BCE. They were the beginning of a new approach to laws where they would be passed by government and written down so that all citizens might be treated equally before them.

powers  are  denied  to the  national governmentin three distinct ways: some  powers, such as the  power  to levy duties on exports or prohibit the freedom of religion, speech, press, or assembly, are expressly  denied  to the  national government  in the  constitution.