Donald Trump wants between the US and Mexico?

The land border between the US and Mexico is 1,933 miles in length, and Donald Trump would like to see all of it sealed off—as would nearly half of all Americans, according to a survey by the Pew Research Center. (At 46%, the share of those who favor putting a fence along the entirety of the US’ southern border has not changed since 2007—although in the latest poll, released Oct. 8, the profile of supporters skewed whiter, older, and more Republican.)

Erecting an end-to-end barrier would be a complicated and costly endeavor, though.

Here’s a look at the fencing that currently runs along roughly a third of the border, based on reports from the US Congressional Research Center (pdf) and the Government Accountability Office (pdf). Most of the fencing was built between 2005 and 2011, although barrier construction along the border dates back as far as 1990 (pdf).

At those costs, the price tag to seal the rest of the border would be between $2.2 billion and $8.3 billion—although the final tab could be much higher because some of the areas that remain unfenced are remote and inhospitable, and presumably would be more expensive to build on.