In the United States, border police have discovered an elaborate tunnel used by criminals to smuggle drugs across the California-Mexico border. The tunnel, which is more than 500 meter, is equipped with a rail system, ventilation and lighting. Inside, police found more than 20 tonnes of marijuana. Police say drug traffickers build the tunnels to bypass stringent controls aimed at curtailing the cross-border trade in illegal drugs and guns. In 2006, police discovered a 731meter tunnel, the longest found so far, also linking Otay Mesa with Tijuana.