Pedestrians walking along Prague's Charles Bridge could be forgiven for thinking they have stepped back into medieval times this weekend, as a giant replica crane moves statues on the bridge's tower. The statues of St. Vitus, St. Venceslas, King Zikmund and King Charles IV were placed on the tower in the 1970's. They were made from concrete, and replaced the rare original sculptures from the 14th century. The 14th century sculptures are now in the Prague Lapidarium, part of the city's National Gallery. With the 1970's reconstructions becoming damaged by pollution and looking substantially different from the sandstone base of the tower, it was decided to replace them. And according to the experts, a recently constructed replica of a medieval crane, was the best way to do it. "After lowering the first few statues we find out that out chosen technology was right. It's the best technology to be used here, because it is very precise, it allows movement of the statues millimetre by millimetre, very slow and fluent," said the crane's developer, Petr Ruzicka. At the top of the tower, the crane is a striking site as it gently lowers the statues. The crane weighs 2500 kilograms and it can carry about 1000. It can easily be taken apart and moved to awkward places, such as the top of a tower. And it is environmentally friendly - functioning with the help of two people walking inside giant wheels, like mice. Built earlier this year, the crane was constructed after Ruzicka studied medieval paintings. The new statues taking their place on the bridge have been made from sandstone, to match the tower. Sculptor Tomas Rafl and his wife Ruzena have been working on them for four years, after studying the originals. Rafl does his final work in preparing the statues before trusting them to the crane. "The difficulty of this work is, that the statues are not standing on any pedestal," Rafl said. "They are just attached to the architecture, directly into the facade. And above them there are gothic architectonic components, which must not be damaged in any way," he said. The statue exchange is expected to continue until Sunday (November 12).