65 concrete pillars with 62 steel doors, each 42 metres wide. The parts were constructed in a dry dock. The area was flooded and a small fleet of special construction ships lifted the pillars and placed them in their final positions. Each pillar is between 35 and 38.75 metres high and weighs 18000 tonnes. The dam is designed to last more than 200 years. The Oosterscheldekering is sometimes referred to as the eighth Wonder of the World. It has been declared one of the modern Seven Wonders of the World by the American Society of Civil Engineers. Construction fleet Four ships were custom designed and built for this project: Mytilus, a ship equipped with various ground working tools, such as needles to make the seabed denser and more stable. Cardium, a ship to transport and lay a special foil carpet on the seabed for the pillars to rest on. Ostrea, a ship capable of lifting a concrete pillar from the dry dock and placing it accurately on a special foil on the seabed. The ship is 85 metres long and has a portal 50 metres high. The ship can only lift 10,000 tonnes, but as a large part of the pillar is underwater, it is not necessary for the ship to be able to lift the full 18,000 tonnes. This ship is considered the flagship of the construction fleet, mainly because of its larger size and power in comparison to the other ships. Macoma, a ship that works closely with the Ostrea, cleaning the foil assisting in placing the pillars accurately in their final position. The ships are named after various types of shellfish. Operation The dam is manually operated but if human control fails, an electronic security system acts as a backup. A Dutch law regulates the conditions under which the dam is allowed to close. The water levels must be at least three meters above regular sea level before the doors can be completely shut. Each sluice gate is closed once a month for testing. Emergency procedures are tested on pre-scheduled dates. Once the test is passed, the shutters are quickly opened again to create a minimum amount of effect on tidal movements and the local marine ecosystem. It takes approximately one hour to close a door. The cost of operation is €17 million per year. The full dam has been closed twenty-eight times since 1986, due to