A crew from a maintenance company removed the black paint on Tuesday and the Vigeland Museum is still not sure how much the incident will cost them.
"It isn't the money that is the main problem, but the possibility of permanent damage to the figures," said special consultant Guri Skuggen at the Vigeland Museum.
Vandalism and tagging is hardly unknown at the massive outdoor sculpture park that is one of the country's best-known landmarks, but until now it has been a minor problem.
"By and large taggers do not go after the figures but the bases," Skuggen said.
The vandals have likely had to use a ladder or some other implement to get high enough, since even the lowest sculptures on the Monolith are out of reach.
"The tagging was discovered Tuesday morning, so it had to be done Monday evening or very late that night," Skuggen said.
Police are investigating the incident but have few clues. Instead of the usual signature at the scene of a conventional tagging the Monolith figures appear to be simply painted black.
The base had the word 'integration' sprayed on it in Norwegian, and had been applied with the use of a stencil.
The Vigeland statues have been the object of political protest before, though in harmless form. Many of them were gagged with white cloths as part of a demonstration against a World Bank meeting in Oslo in 2002.
