The remains of 12 dogs were buried together in a pit more than 500 years ago in what is now Mexico City, archaeologists said Friday. The dogs were buried in a single pit about 6-feet square. Rocio Sanchez Morales, with the National Institute of Anthropology and History, said the burial is unusual because dogs in that period were usually buried with humans or at building sites to serve as escorts to the underworld, as offerings or as guards. The dogs are believed to have been buried sometime between 1350 and 1520, when the Aztec Empire was at its height. The pit was excavated during salvage archaeology before new construction in the area. A biologist, Alicia Padilla White, examined the skeletal remains and said they appear to have been common dogs -- what might today be called mutts, Antonio Zamora, one of the archaeologists on the dig, said.