Sporadic screams turned to a collective roar, as word trickled through the crowd that the popemobile was near.
People staked out spots on ladders, roofs, their fathers' shoulders.
"Se ve, se siente. El Papa está presente!" they chanted. "You can see it, you can feel it. The pope is present!"
Francisco Valdez, 24, who traveled 12 hours from Monterrey, slept outside Saturday night, hoping for the best spot to catch a glimpse of the pope. He claimed a space near the front of the crowd, waiting with his cellphone hoisted.
As the pontiff neared, a woman broke into sobs, and Valdez hit the record button on his phone. With a whir, Pope Francis had passed.
"He went so fast!" Valdez shouted. "Still, wow."