Then, Gendron hit something.

“We started digging around and we uncovered the top of it. I knew what it was. I’ve hit one before,” he said.

It was a historic, underground cistern, put there around 1869 for fire protection.

The cistern, or reservoir, is basically an old-fashioned water hydrant. The one Gendron discovered is about 20 feet in diameter, 16 feet wide, and held 40,000 gallons of water.

After finding it, Gendron stopped work and notified Lewiston Public Works Director Dave Jones.

“The craftsmanship of the brick work is totally amazing, especially considering the times and the tools our forefathers used,” Jones wrote on Facebook after inspecting the find.

On Wednesday, Gendron showed off the cistern, uncovered and deep in the ground, to a reporter and photographer.

It’s a cool piece of history, he said.

The cistern is made of red brick. It was full of water when they found it.

“It was clear,” Gendron said. “You could see right to the bottom. It didn’t leak.”

Nearby on a sidewalk is a type of manhole cover where for some 150 years water was taken out or poured in.

“They must have filled it because there are no holes to where the water could get in from anywhere,” Gendron said.

He should know.

The cistern was uncovered and the dirt around it was cleared. His crews cut a hole in the side and, after the water was drained, Gendron crawled in. With a light, he took photos of the red bricks and mortar.

“It’s beautiful. It’s more impressive inside than outside,” he said.

Gendron joked that he’s called a cistern expert.

“People who have been doing this for a long time have never seen one. I’ve seen three,” he said.

Years ago he excavated one on Main Street, another on College Street.

“It’s always in the old parts of town,” he said.

Doug Hodgkin, retired Bates College professor who has written several books about local history, agrees.

Underground cisterns were built to hold water to fight fires before running water.

“It was only in the 1870s that Lewiston started providing water through pipes buried in the city,” he said. Initially, Lewiston got its city water from the Androscoggin River above the falls. Later, Lake Auburn became the water supply.

Lewiston’s underground cisterns were installed between 1856 and 1870.

Water supplies were needed because at that time fire was a serious concern, more so than today. In residential areas, buildings were constructed of wood and built close together. If a fire started, it could easily spread from one building to the next causing serious damage, Hodgkin said.

“For example, the courthouse on Lisbon Street was constructed as a theater in the 1870s. Before that, four or five buildings there burned, and opened up space for a new theater,” Hodgkin said. “Fortunately Lewiston never had a real conflagration like Portland did” in 1866.

A conflagration is a huge fire that destroys an extensive amount of land and property.

In 1860, Lewiston had dirt streets.

The areas where Gendron uncovered the cistern — Spring, Winter and Summer streets behind Central Maine Medical Center — were just being developed then.

Laborers built the canal and underground cisterns, along with other city infrastructure. The mills were running. Irish and French Canadian immigrants were here and more were arriving every day. In those days immigrants had large families.

“Lewiston’s population was exploding,” Hodgkin said. “The population was doubling from census to census. It would double from 1850 to 1860” and double again in 1870.

With buildings that could easily burn built so close together, insurance companies pressured cities to reduce the risk of fire losses, Hodgkin said.

“They said if you don’t do something, insurance rates would be high,” he said.

It was common practice to install underground water tanks, he said.

The Spring Street cistern will stay where it is. A pipe will be installed and run through it.

Gendron is installing pipes to separate stormwater runoff from the sewer system to prevent sewage from entering the Androscoggin River during heavy storms. The job will continue through November.

“I hope I don’t hit another one,” Gendron said.