Two masked armed robbers tied up a museum guard at the birthplace of the ancient Olympics in southern Greece and made off with dozens of artifacts, authorities said Friday. Greece's Culture Minister Pavlos Geroulanos submitted his resignation after the robbery at the antiquities museum in Ancient Olympia, but it was unclear whether it had been accepted by Prime Minister Lucas Papademos. Geroulanos was traveling to Olympia on Friday. Police set up roadblocks in the area as part of a broad search to try to locate the robbers, who wore ski masks. Museum authorities and police did not have an immediate account of the items taken from smashed display cases, but local authorities and police said about 60 artifacts are estimated to have been snatched. "According to the results of the investigation so far, unknown persons, this morning, at about 07:34 a.m., immobilized the guard of the museum and removed bronze and clay objects from the displays, as well as a gold ring," a police statement said. Olympia Mayor Efthimios Kotzas urged authorities to improve security at the site. "The level of security is indeed lacking," Kotzas told state-run NET television. These are treasures. A piece of world heritage has been lost thanks to these thieves ... I think (authorities) should have been more mindful and the security should have been more serious. Friday's robbery is the second major museum theft in the past two months in Greece. In January, thieves made off with art works by 20th century masters Pablo Picasso and Piet Mondrian from the country's National Gallery in central Athens. In that pre-dawn heist, the burglars also took a pen and ink drawing of a religious scene by Italian 16th century painter Guglielmo Caccia. A fourth work by Mondrian also was removed from the National Art Gallery in one of the best-guarded areas of central Athens, but the thieves abandoned it as they fled.