The 24km (15 mile) subway line will connect several Mexico City suburbs and is due to open in 2012. Historians knew that these areas had been built over the top of the original Aztec settlements (much of inner Mexico City is), but no-one knew that the remains were down there.
Maria de Jesus Sanchez, an archaeologist from the National Institute for Anthropology and History, revealed, "In total, there are 60 graves, 10 adults and around 50 children of different ages, some two or three years old." It was common practice for Aztec burials to take place under the foundations of their homes. Deceased children were often placed into earthenware pots, as this aped the shape of the womb.
Also amongst the finds were pottery shards, a 50cm (1.6ft) statue of a woman and a facial stone carvings. The skeletal remains date back to around 1100 to 1500 CE, while the carvings could be as much as 2000 years old.
These discoveries have been made periodically since work began on the subway line, in September 2008. The suburb of Culhuacan has proved to be a hotspot for them. Each time a new item is found, work stops immediately while the archaeologists swoop in to excavate. Such practises are a modern development. In the past, the construction workers just plunged on and historians fear that many sites of archaeological importance were destroyed.
Mexico City was once the heart of the Aztec empire, under its former name of Tenochtitlán. The city's Aztec nickname, Mexico, ultimately provided a name for the whole country.