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Mexico City has existed in one form or another since the Aztecs settled here in 1315, but the colonial city founded by the Spanish with a grid system of streets was born out of the bloody conquest of 1521.

As those streets — among the oldest in the hemisphere — near their 500th birthday, two Mexican writers are trying to peel back the layers of change that have hidden their colorful history.

Three years ago, Hector de Mauleon and his main ally, Rafael Perez Gay, persuaded the city government to erect plaques on downtown street corners to give passers-by some description of famous past residents or notable events.

The plaques are made of a decorative colonial-style pottery known as Talavera and are carefully affixed to oft-historic facades of buildings.

In a metropolis where so much occurred and still happens on the streets — markets, protests, art, performances — it is a way of recovering the city's history.

So far, they have plans to create 200 of the plaques, but the process of installing them is just starting and may expand to other neighborhoods, like the southern district of Coyoacan, where Spaniard Hernan Cortes set up his government soon after conquering the city.

De Mauleon recalls walking when he was young along the downtown streets with his grandfather.

"He very much liked to take walks and remember what had been there before," De Mauleon said. "I would accompany him and it was like taking two trips at once: the one we were on at that moment, and the one about things that had happened long ago, or were no longer there."

But it's hard if you don't know what you're looking for. Starting around 1921 — the 100th anniversary of Mexico's independence — the government changed most of the old street names.

Many of the streets were named for Latin American countries like Brazil, Chile or Argentina in a sign of the government's gratitude for them sending representatives to meet embattled President Alvaro Obregon during the centennial, at a time the country was still roiled by periodic uprisings in the wake of Mexico's bloody 1910-1917 revolution.

"The original name of Brazil Street, for example, was 'the Sepulcher of Santo Domingo.' That was a beautiful name," De Mauleon said.

Other streets were renamed to honor fallen heroes of the revolution or dates of key battles. The original names gradually were forgotten.

"When they did that, they severed the collective memory," De Mauleon said.

Not surprisingly for a city this old, it isn't the first attempt to put historic markers downtown. In 1928, a group of intellectuals asked authorities for permission to set up plaques — some of which are still visible — often with just the original names of the thoroughfare.

But memories of more than just nomenclature have faded. One planned plaque will mark the location of a hotel that was taken over by U.S. troops during the 1846-48 Mexican-American war.

Mexico City was founded at a time of transition in Europe, when the old continent was emerging from the centuries-old guild systems that prevailed in the Middle Ages.

Originally Mexico City had something of a guild influence as well. All tradesmen from a certain craft — for example, metal workers or shoemakers — were assigned a different part of the city to do business, or often an entire street. Remnants of that history remain.

De Mauleon stands in the city's main square, the Zocalo, in the shadow of the massive cathedral and the Baroque city hall, near the excavation that reveals part of a pre-Hispanic Aztec pyramid.

He points to an old, arcaded building on one corner that seems to be populated by nothing but shops that buy or sell gold and jewelry. This was once the neighborhood assigned to goldsmiths, he notes.

"Every street got its name for one of three things — because there was a building there that gave it that name, like a convent or a church," de Mauleon noted. "Or some important person lived there, or something important happened there that deserved to be remembered, like a legend."

Over the years, a gradual dusting of change obscured much of the history. De Mauleon points out a restaurant that used to be a drug store — and was also the spot, in 1896, that the first moving picture was shown in Mexico.

The city is full of legends, or used to be, when people were attuned to them.

"In those days you could go for a walk and you would realize the city was talking to you, it was telling you about its past," De Mauleon said.