Why do Wonders of The World come in Seven?

The Seven Wonders of the Ancient World

The Great Pyramid of Giza
The Hanging Gardens of Babylon
The Temple of Artemis at Ephesus
The Statue of Zeus at Olympia
The Mausoleum at Halicarnassus
The Colossus of Rhodes
The Pharos of Alexandria

The Seven Wonders of the Medieval Mind

Stonehenge
The Colosseum
The Catacombs of Kom el Shoqafa
The Great Wall of China
The Porcelain Tower of Nanjing
The Hagia Sophia
The Leaning Tower of Pisa

The Seven Natural Wonders of the World

Mount Everest
The Great Barrier Reef
The Grand Canyon
Victoria Falls
The Harbor of Rio de Janeiro
Paricutin Volcano
The Northern Lights

The Seven Underwater Wonders of the World

Palau
The Belize Barrier Reef
The Galapagos Islands
The Northern Red Sea
Lake Baikal
The Great Barrier Reef
The Deep Sea Vents

The Seven Wonders of the Modern World

The Empire State Building
The Itaipú Dam
The CN Tower
The Panama Canal
The Channel Tunnel
The North Sea Protection Works
The Golden Gate Bridge

The Seven Forgotten Natural Wonders of the World

Angel Falls
The Bay of Fundy
Iguaçú Falls
Krakatoa Island
Mount Fuji
Mount Kilimanjaro
Niagara Falls

The Seven Forgotten Modern Wonders of the World

The Clock Tower (Big Ben)
Eiffel Tower
The Gateway Arch
The Aswan High Dam
Hoover Dam
Mount Rushmore National Memorial
The Petronas Towers

The Seven Forgotten Wonders of the Medeival Mind

Abu Simbel
Temple Angkor Wat
Taj Mahal
Mont Saint-Michel
The Moai Statues
The Parthenon
The Shwedagon Pagoda

The Petronas Towers was in the list above but not The Leaning Tower of Pisa, The Forbidden City, The Sydney Opera House, The Esplanade, The Statue of Liberty, The Mayan Temples, The Temple of the Inscriptions, The Throne Hall of Persepolis, Petra, The Suez Canal or The Red Fort in India.

Have anyone ever wonder how the list was established?


Source: http://wonderclub.com/AllWorldWonders.html