The protestors were physically removed with “direct force” after they failed to clear the entrance to the construction site to allow heavy machinery into the area, police said on Thursday.
While opponents said that some 1,000 demonstrators showed up to the site, police said they had counted about 500. After they were moved from the street, only 30 or 40 remained by 5am on Thursday, police said.
“It was a quiet night,” one officer said.
The incident followed last Friday's much larger protest by about 20,000 people, who formed a human chain around the building before marching to city hall to demonstrate against the €4.1-billion project, which is set to revamp the historic station in the southwestern city.
Stuttgart 21 has been widely criticised because it will tear up the city centre for more than a decade and demolish parts of the landmark train station built by architect Paul Bonatz in 1928. Supporters argue it will make the city an important rail link between Eastern and Western Europe.
The old terminal will be transformed into a spacey underground station where trains do not have to back out to continue their journey. Transforming 100 hectares of central Stuttgart and digging 57 kilometres of tunnels, it will be one of Europe's biggest construction sites.
But there have been weeks of protests against ballooning costs and the destruction of part of the historic terminal building.