On Friday, President Trump's administration released details from a division of the US Department of Homeland Security outlining the requirements for Mr. Trump's promised wall along the US/Mexico border. The details for the project, provided by Customs and Border Protection (CBP), are meant to serve as guidelines for contractors who will submit their proposals for the first phase of the structure on March 29.

The requirements for the wall actually come in two sets; the first includes guidelines for a solid concrete structure and the second set is for a wall with "see-through" components that would likely be more affordable or have other "operationally advantageous" components over its concrete counterpart.

"The wall design shall be physically imposing in height," the CBP outlines say, calling for a nominal height of 30 feet. However, the proposals also noted that designs as low as 18 feet would also be acceptable. The proposal also requires 25- and 50-foot automated gates in certain parts of the wall's design to accommodate vehicles and pedestrians.

In addition to these height requirements, the CBP also states that the wall should continue about six feet underground to discourage tunneling, be designed in such a way so that climbing the structure without a ladder would be impossible, and be able to withstand at least an hour's worth of attempts to break through from a "sledgehammer, car jack, pick axe, chisel, battery operated impact tools, battery operated cutting tools, Oxy/acetylene torch or other similar hand-held tools." The requirements also note that "The north side of wall (i.e. US-facing side) shall be aesthetically pleasing in color, anti-climb texture, etc., to be consistent with general surrounding environment," though no aesthetic suggestions were put forward for side facing Mexico.

The contract for the wall will be awarded based on 30-foot-wide prototypes and 10-foot by 10-foot mockups that will be built in San Diego.

"It's a way for the agency to identify designs," a CBP official told NPR. "We're looking for industry's designs, to take a fresh look at the wall. We'll have industry propose and then we'll down-select."

The border wall idea has been heavily criticized by Democrats and some Republicans for its intent as well as its projected cost.

Trump has said the wall would cost around $12 billion, while Congressional Republicans tend to put the figure somewhere between $12 and $15 billion. Other cost estimates have been even higher, with a recent MIT study estimating a massive $38 billion price tag for the structure. A budget proposal released earlier this week by the Trump administration would include a $2.6-billion down payment on the wall, which would cover only a fraction of the most optimistic cost projections.

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There are already some 700 miles of extant fencing along the border that would have to be replaced by the new wall. Some of these structures are 15-foot steel posts placed inches apart, which are designed to keep humans from slipping through, and other portions consist of shorter structures designed to block cars from crossing the border. In total, the new wall would have to cover the entire US-Mexico border, which is about 2,000 miles long.

This article contains material from the Associated Press.