The German town of Plettenberg admitted on Saturday that five Jewish memorial stones had vanished after contractors dug up the pavement.

Germany recently marked the laying of its 75,000 Stolperstein (stumbling block) — name-engraved bronze cubes embedded mainly outside former Jewish homes.

Trenching was done early last year at the address Alte Markt 3, formerly home to the Heilbronn family. In 1942, parents Helene and Alex were murdered at Treblinka; their children Egon, Jenni and 5-year-old Hannelore at Zamosc.

Read more: 75,000th 'Stolperstein' for Holocaust victims laid in Germany

The cubes' apparent disposal at a local site for building waste was made public this week by a local historical association, said a local portal of the Märkische Zeitung newspaper for the Lennetal valley in North Rhine-Westphalia (NRW) state.

But this came out only after Mayor Ulrich Schulte had taken part last Monday in a remembrance event for Holocaust victims at Plettenberg's Jewish cemetery, said the portal's author Johannes Opfermann.

'Very annoying'

Schulte went on to describe the loss as "very annoying," and the city's building director Sebastian Jülich said the ground works firm — subcontracted by a telecommunications concern — had paid €280 for each replacement cube and the still-awaited installation.

"The most important thing is that stones are replaced in the [cobblestone] pavement," said Mayor Schulte, adding that he regarded the engraved cubes as a very important way to remember the victims of the Nazi era.

Last year, while the cable was trenched into the cobbled pavement, both the project supervisor as well as the contracted firm had been told "many times" about the monuments, Jülich said.

'Disposed of'

That unfortunately didn't work; the stones were disposed of," said Jülich, adding that cubes at other trenching sites had been taken into safekeeping during cable-laying.

Read more: Nazi victim memorial stones stolen in Berlin (2017)

Beginning in 2015, the city with a population of 25,000, had 13 cubes laid in memory of its late Jewish residents, as part of a decadeslong remembrance project led by the Cologne-based artist Gunter Demnig.

Plettenberg's city marketing association says the cubes, including those laid at the Alter Markt (Old Market) by Demnig in 2015, were donated by the trade union IG Metall and pupils of the Gertrud Bäumer vocational college in neighboring Ludenscheid.

Engraved by hand in 24 languages

Supplying the stumbling stones since 2005, Michael Friedrichs-Friedlaender, a sculptor specialized in metals, has been delivering them from his Berlin workshop to 26 European countries, with the engraving done by hand in 24 different languages.

Embedded into each cube, measuring 9.6 square centimeters (3.8 square inches) and weighing 2 kilograms (4.5 lbs), is an engraved bronze cap.

Starting with the words "Here lived," the plaque then records the victim's name, date of birth and a date alongside such words as "deported," "murdered," "disappeared" or "forced to flee."

Stolperstein monuments, place in memory of Jewish residents, politically persecuted people, Roma and Sinti, homosexuals, Jehovah's Witnesses and "euthanasia" victims, are now displayed in some 1,200 cities and communities across Germany.