We all know to back up our files and photos, but what about our castles and churches? CyArk, a nonprofit organisation, has created digital copies of more than 100 of the world's best-known monuments, mapping Roman ruins, ancient statues, and even an entire island. Now it plans 400 more, with the goal of digitally preserving the world's most important sites against war, wear, and the impact of climate change. "There is never going to be enough time or money to preserve everything," CyArk co-founder Barbara Kacyra said on Monday at a launch event at the Tower of London. "If you can't physically save something, your next best thing is to digitally preserve it." California-based CyArk works by using 3-D laser scanners, radar, and a host of other technologies to create detailed maps of famous monuments - from Mayan pyramids in Chichen Itza to the Leaning Tower of Pisa - measuring nooks and nicks with millimetre precision. Not only do the lasers capture minute damage invisible to most cameras, the 3-D data can be used to create hyper-realistic models used by tourists and educators. Master copies of the measurements are kept by Iron Mountain, which stores some 2 petabytes' worth of data on magnetic tape in its secure underground archive at the bottom of a former limestone mine in the US state of Pennsylvania. A petabyte is a million gigabytes. Kacyra said the project was born out of the heartbreak of seeing the Taliban demolish giant Afghan Buddha statues in 2001, but Gustavo Araoz, a senior preservationist who is helping CyArk draw up a list of its next 400 sites, said similar destruction was playing out in slow motion across the globe. "This happens every day at a smaller and much less dramatic scale," he said. There is already some evidence that the preservation project is paying dividends. Ugandan diplomat Sam Muhwezi said that a 3-D model drawn up by CyArk was being used to help restore the country's fire-damaged royal tomb complex. "It's the perfect example of why this kind of project is important," he said.