Talk of ancient tunnels in the Mexican city of Puebla has long been considered urban legend. But authorities have now confirmed their existence, and say the secret passageways could date back 500 years. The city hopes to turn the tunnels into an attraction.

The underground passages, which measure approximately seven meters high and three meters wide, were discovered during public works in the colonial city.

"In the urban narrative or urban legends there was word of the tunnels in Puebla, but nobody knew where they were, they had never been seen,” Sergio Vergara Bermejo, manager of the Cultural Heritage and Historical Center of Puebla, told El Universal.

#Entérate: Hallan casas y fósiles de dinosaurios en túneles de Puebla http://t.co/cjdfQdJ0Dxpic.twitter.com/jxy2w9IDnp — Milenio Novedades (@MilenioYucatan) September 4, 2015

Four separate entrances to the tunnels were found. The routes run from Fort Loreto to the Fort of Guadalupe, from Fort Loreto to the district of San Jose, and from Fort Guadalupe to Los Remedios Church, where the defense of Puebla took place against the invading French Army in 1862.

The tunnels are believed to date back as early as 1531, when the city was founded. Many more are believed to exist.

“They are from the foundation of the city,” Vergara said, adding that they were likely old drainage tunnels.

Vergara also said that an old bridge had been discovered, which was apparently buried after the city flooded centuries ago.

All the underground structures are filled with mud and silt, and must be excavated.

En las ciudades de México se habla de "tuneles" secretos. En Puebla acaban de descubrirles http://t.co/Ozz4kUwBJQpic.twitter.com/VJTHUUWigi — Gabrielgtzg (@Gabrielgtzg) September 2, 2015

Puebla's mayor, Tony Gali, has designated five million pesos (US$295,000) for the restoration of the tunnels. The city hopes to transform the discoveries into a tourist attraction.

The exact location of the tunnels is currently being kept a secret.

It's not the first time that tunnel-like structures have been found in Puebla, some of which are believed to have been trenches or defensive works from the 1862-1863 battles between Mexico and French forces.

Founded around 1531, Puebla is one of the oldest cities in Mexico, and considered to be among the five most important Spanish colonial cities in the country. It was named a UNESCO World Heritage Site in 1987.