Engineers at work on the Costa Concordia ahead of the start of the salvage operation on September 16, 2013 in Isola del Giglio, Italy. (Marco Secchi/Getty Images)
(WXIA) -- An historic attempt is underway to pull the crippled Costa Concordia to shore.
After months of preparations, engineers are using a system of 36 pulleys and counterweights to free the ship from a seabed.
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Experts say the Costa Concordia is the largest cruise ship to ever require such an operation. The effort is expected to take about 12 hours.
The ship crashed into a reef off Italy's Tuscan coast last year, killing 32 people.