A rail line construction site in Mexico City -- that yielded an exceptional discovery.

Archeologists uncovered the remains of 50 Aztec children, some of them stuffed into clay pots for burial.

The Aztecs believed the pots resembled a mother's womb, keeping the children warm.

Archeologist Maria de Jesus Sanchez said there were 60 graves in all, ten of adults and around 50 of children of different ages.

Also found were pots and plates, dating back to between 1100 and 1500 AD, the eve of the Spanish conquest.

[Maria de Jesus Sanchez, Archeologist]: (Spanish)
"It indicates to us that the area had been occupied continuously since very early times. Considering that there are marks on the bones, those types of things will enable us to learn more about these people and the population that lived in this area."

The new metro line links several former Aztec towns which have existed for centuries but have been swallowed up into the city's suburbs.

The Aztec empire held sway over a large part of Mesoamerica for hundreds of years before the arrival of the Spanish.

So modernizing Mexico's cities could produce more historic finds.