A mass grave containing the bodies of up to 800 babies has reportedly been found near a former home for unwed mothers in Ireland.

The children were likely buried in secret in a concrete tank alongside the St. Mary's Mother and Baby Home, which was run by nuns in Tuam, Galway for a period of 36 years. The home closed in 1961.

Newly-discovered reports show that many of the children died from malnutrition and neglect, or from complications associated with measles, pneumonia, TB, gastroenteritis, and other diseases.

Local historian Catherine Corless uncovered the grave and is part of a group pushing for an investigation and a memorial to mark the site, which is now surrounded by a housing estate.

The mass grave is the latest and most shocking development in the home's dark history. Local health board inspectors reported horrifying conditions after a visit to the home in 1944. At that time, 333 unwed women and their children were living there, far exceeding the home's capacity of 243.

Most children were between the ages of 3 weeks and 13 months. They were "fragile, pot-bellied and emaciated," according to the inspectors' report. One of them, a 13-month-old boy, had "no control over bodily functions" and was "probably mentally defective."

A 1932 ad from a local newspaper offers a chilling glimpse into that world.

Children's Home Tuam: Contract for Coffins (Connaught Tribune, 30 Jan, 1932): pic.twitter.com/skBTbnDuAW — Shane (@scary_biscuits) May 27, 2014

Homes for unwed mothers were common in Ireland during the late-19th and early-20th centuries.

Another such home, Sean Ross Abbey in Tipperary, was depicted in the Oscar-nominated flim "Philomena." The film tells the true story of Philomena Lee, a young Irish woman was staying in an Irish home for unwed mothers in the 1950s when suddenly one day the nuns took her 3-year-old son and adopted him to an American couple.

That was one very tragic story. Now we have 800 more.

The "outside nursery" at Sea Ross Abbey. (Brian Lockier/Adoption Rights Alliance)

Children in the play room at Sean Ross Abbey. (Brian Lockier/Adoption Rights Alliance)

The tea room at Sean Ross Abbey. (Brian Lockier/Adoption Rights Alliance)

Nuns stand over the cribs of small babies at Sean Ross Abbey. (Brian Lockier/Adoption Rights Alliance)