Greg Zanis, of Aurora, Ill., began putting up the crosses Sunday on a hill across the street from the theater in Aurora.
Aurora Mayor Steve Hogan arrived later, put his hand on a cross and said a prayer with Zanis. Hogan became emotional and embraced his wife.
The crosses are white, about 3 ½ feet tall and made out of lumber. Zanis says he was swamped with requests to bring them.
The 15 crosses Zanis erected near Columbine included two for the killers, Eric Harris and Dylan Klebold. The father of one of the victims tore those two crosses down.