Set to stretch 170 kilometres across northwest Saudi Arabia, the megastructure, which will have mirrored facades, will be 500 metres tall, but only 200 meters wide.
Planned as part of the Neom development, The Line was designed as a dramatic alternative to traditional cities that typically radiate out from a central point.
Although it has not been officially announced, Dezeen understands that the megastructure was designed by US studio Morphosis.
"At The Line’s launch last year, we committed to a civilizational revolution that puts humans first based on a radical change in urban planning," said Saudi Arabia's crown prince Mohammed bin Salman.
"The designs revealed today for the city's vertically layered communities will challenge the traditional flat, horizontal cities and create a model for nature preservation and enhanced human livability," he continued.
"The Line will tackle the challenges facing humanity in urban life today and will shine a light on alternative ways to live."
The structure will consist of two wall-like structures that will enclose an open area between them.
At 500 metres high the pair of structures will become the 12th highest building in the world, as well as being by far the longest.
The structure, which was designed to house nine million residents when it is complete, will contain residential, retail and leisure areas as well as schools and parks.
The different functions will be stacked in an arrangement described by the city's creators as Zero Gravity Urbanism.
Visuals show parks placed between the two linear blocks, which will be connected by multiple bridges and topped with more green spaces.
It will be entirely clad in mirrored facades to give the structure a unique appearance.
"The Line will have an outer mirror facade that will provide its unique character and allow even its small footprint to blend with nature, while the interior will be built to create extraordinary experiences and magical moments," said the Saudi Arabian government.
A transport system running the length of the megastructure would be designed to connect both ends of the city within 20 minutes.
According to the Saudi Arabian government, the structure will be entirely powered by renewable energy and was designed as a sustainable alternative to traditional cities.
"We cannot ignore the livability and environmental crises facing our world's cities, and Neom is at the forefront of delivering new and imaginative solutions to address these issues," said Bin Salman. "Neom is leading a team of the brightest minds in architecture, engineering and construction to make the idea of building upwards a reality."
"Neom will be a place for all people from across the globe to make their mark on the world in creative and innovative ways," he continued.
The Line, which was first revealed last year, forms part of the Neom initiative in northwest Saudi Arabia. Neom is part of Saudi Arabia's Vision 2030 drive to diversify its economy and become less reliant on oil.
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