Donald Trump is not the first U.S. president to suggest the nation needs greater security on the U.S.-Mexico border. However, Trump made this issue a central campaign topic, and he proposes building a wall to keep people from crossing into the U.S. illegally.

"The wall," as it is now widely referred to, has made progress in fits and starts since Trump took office in 2017. There has been recent attention on the topic since the announcement that thousands of National Guard troops will be moved to the border as a security measure.

A move like this comes on the heels of deeply partisan activity surrounding the wall. It was originally Trump's idea to have Mexico fund the wall, to no avail. Congress only approved $1.6 billion for the project, when Trump wanted $25 billion. Democrats wanted to exchange amnesty for 1.8 million DACA-eligible immigrants in exchange for wall funding, but Trump rejected this offer.

All of this political wrangling has slowed progress, but it didn't keep Trump from whittling a list of 200 potential contractors interested in building the wall down to a handful that have submitted prototypes already.

Who are these companies? Caddell Construction of Montgomery, Alabama; Fisher Sand & Gravel/DBA Fisher Industries of Tempe, Arizona; Texas Sterling Construction in Houston, Texas; and W.G. Yates & Sons Construction in Philadelphia, Mississippi; ELTA North America Inc., part of state-run Israel Aerospace Industries; and KWR Construction Inc. of Sierra Vista, Arizona.

In January, these companies' finished prototypes were tested by tactical teams. "Military special forces based in Florida and U.S. Customs and Border Protection special units spent three weeks trying to breach and scale the eight models in San Diego," CBS News reported.

A Customs and Border Protection report summarized that most likely the completed wall would be a by-product of "combined elements of each, depending on the terrain." Pieces will likely be pulled from different prototypes, in a Lego-like fashion.

While the verdict is still out on the exact design, and whether the project will truly move forward, there are key qualities we can expect in any real-world Mexico wall.

The wall will likely be at least 18 feet high and made from extremely durable material — possibly even see-through making it impossible to climb. Steel at ground level topped with concrete is reportedly the desired layout.

W.G. Yates & Sons Construction, Caddell Construction, Texas Sterling Construction and Fisher Sand & Gravel submitted concrete designs. ELTA North America Inc. and KWR Construction Inc. built models from other materials.

In mid-March, Trump traveled to southern California to inspect progress on eight different wall prototypes. However, Trump has thus far neglected to announce any more concrete (pun intended) details about which designs have caught his eye.

For now, it is expected that 100 miles of border wall will be built using allocated funds.

Ronald Vitiello, acting deputy commissioner of U.S. Customs and Border Protection, said March 30 that the wall will function as a "comprehensive solution that provides wall, lighting, enforcement cameras, and other related technology, and all-weather roads to impede and deny illegal cross-border activity."

Most of the proposed wall structure will be built in three parts of Texas: Rio Grande Valley, Hidalgo County and Starr County. Santa Teresa, New Mexico, may also see 20 miles of new border wall, according to current plans.