VENICE: On a manic spree that began last Saturday, an unknown vandal who was quickly dubbed the night hammerer by local newspapers lopped the arms off Renaissance sculptures and hacked at the capitals decorating the Ducal Palace in St. Mark's Square. On Wednesday night, a suspect, a 38-year-old man with a history of mental illness, was arrested after witnesses identified him and the police reportedly found marble shards from the damaged monuments when they searched his home. But for many Venetians, the random destruction wreaked by apparently one man's folly brought home the difficulties of taking care of this ancient city improbably built on water. "You just cannot protect all of Venice's artistic heritage; you can't put everything under glass or put up barriers," said Giorgio Rossini, the chief state official charged with the safeguard of the city's monuments. "We can increase vigilance and we can put more police in the most crowded areas, but otherwise I don't know what else we can do." Perhaps no other city is as much a monument in and of itself as Venice, a picturesque open-air museum precariously perched on a smattering of islands linked by dozens of bridges. Beyond its magnificent palazzi and lavishly decorated churches, the city's magic, as John Ruskin once gushed, is created from the unique meeting of water and stone. All the more reason to worry when that stone is threatened. The vandalism suspect, Antonio Benacchio, whose name was released Thursday when he was formally charged with destroying public property, wielded his hammer on a half-dozen works, according to authorities. Some, like a bas-relief depicting St. Peter and a small terra cotta of a Virgin Mary, were in the remote Castello district, where it was unlikely that he would be caught. The vandal also lopped off the hands of two statues in the Church of the Redentore on Giudecca Island, also not on the beaten track. But most daringly the vandal hacked at a scene depicting Moses receiving the Ten Commandments located on a capital of the loggia of the Ducal Palace in St. Mark's Square, one of the most prominent spots in the city, and was frightened off by tourists on Sunday night. On Monday morning, the vandal tried to damage a crucifix over the main altar of the Church of St. Job, in the Cannaregio district. Priests at the church said they called the police after finding a man standing on the altar trying to reach the sculpture, a 20th-century statue of Christ with hands outstretched. "He said he didn't like it; he said it wasn't normal," said the Reverend Luigi Franzolin, the superior at St. Job. He said that another priest, called the police. "He left his screwdriver and wrench. They're still here," Franzolin said. The priest noted that the church had an alarm system and that at least one person, usually a volunteer, was always in the church during the hours it was open, but he admitted that it was hard to be everywhere at once. "You can miss things," he said. After the fact, Franzolin said he had received a call from the Venice police chief. "He told me he was calling all the churches in the city to keep an eye out for copycat vandals," he said. But the priest had harsh words for the local art authorities, accused of not giving churches enough assistance to look after their art treasures. "They come after us if we move a nail, and we have to answer for damages, but they don't help us with anything," he grumbled. The national culture minister, Giuliano Urbani, congratulated the police on their quick resolution of the case but said that it showed that "there always need be vigilant eyes on our substantial artistic heritage." The minister told reporters that the government was evaluating the best means and initiatives to guarantee control of that heritage, a sentiment often echoed in past months by Interior Minister Giuseppe Pisanu, who has put hundreds of monuments around the country under surveillance to protect them from terrorist attacks. Some Venetian churches have organized into a nonprofit consortium, Chorus, whose aim is to contribute to the safeguarding and restoration of members' artworks. There is an admission fee to the 15 churches that form part of the consortium, used in part to cover the costs of surveillance during the churches' opening hours. Franzolin said that St. Job would consider joining. "In the end, are we just going to have to replace originals with copies so that we don't have to worry about the damages?" asked Daniel Berger, a consultant with the Culture Ministry and with Venice City Hall. He cited a number of art works safely ensconced in museums, far from the ravages of man and climate. "Maybe that's the future," he said.