Of the 1,933 miles along the US-Mexico border, 1,279 miles is unfenced. From western California to eastern Texas, across four US states and 24 counties, the border criss-crosses arid desert, rugged mountains, and winding rivers. 7.3 million people live in the border counties on each side of the line. In an effort to make good on campaign promises to ‘build that wall,’ President Trump refused to back down on his demand that Congress allocate $5.7 billion for the project, plunging the government into a shutdown after Senate Democrats refused to back a spending bill that included the wall funding. The longest contiguous stretch that is unfenced is in the center of Texas and it is more than 600 miles long. There are no cities on either side of the wall here, and the Rio Grande river forms part of the border. The original border fence construction was created with consideration to geography, economics and also legal factors. In 2006, Congress required that a barrier be constructed but the project was never completed as mandated, and much of the border fence lies in disrepair. The Texas border is mostly unfenced due to treaty provisions and property rights. Fencing was easier to construct in California, Arizona and New Mexico because the Federal Government controlled more of the land adjacent to the border. The cost estimates for constructing a new border fence have ranged from $8 billion (President Trump’s initial campaign trail estimate), to as high as $40 billion. The number most often quoted by political and construction experts, is between $15 and $25 billion. To replace what exists with what has been described as a 20 to 50 foot structure that will traverse 1,000 of the some 2,000 miles of the U.S.’s border with Mexico will be no easy feat.