Altiplano is a high-security prison in Almoloya de Juarez, Mexico. The maximum security federal prison was built with walls that are as much as 1 meter in thickness and the air space near the facility is restricted. Authorities claim that cell phone transmissions are limited within 10 km (6.2 mi) of the prison to stymie communications between the inmates and their colleagues outside. Additionally, armored personnel carriers are based near the facility to protect it against a potential assault. This prison was thought to be impenetrable until the July 11, 2015, when "El Chapo" Guzmán escaped through a tunnel.