In 2015, the Hungarian government constructed a barbed wire fence along its border with Croatia to stop hundreds of thousands of refugees from the Middle East and Africa who were illegally entering Hungary. Hungary completed the fence and closed this border on October 16, 2015. According to data from the Hungarian national police, migrant captures, which is a proxy for arrivals, declined by more than 99% within two days and stayed at this level through the rest of the year. Association does not prove causation, but the timing and abruptness of this decline suggest that the fence played a major role in it. Similar changes have occurred in other places where border barriers have been implemented, including areas of the U.S. and Israel.