What modern day city is located where the Aztec capital was

Tenochtitlan

Explanation:

Tenochtitlan, also known as Mexica-Tenochtitlan, was a large Mexica altepetl in what is now the center of Mexico City. The exact date of the founding of the city is unclear. The date 13 March 1325, was chosen in 1925 to celebrate the 600th anniversary of the city.

lying without the limits of the several states; and may permit them, at such times, and in such manner as it

a big wall across the mexican border so no drugs, terrorist, or illegal immigrants can come through : )