A wall stain that some believe depicts the Virgin Mary drew scores of faithful on Thursday to a gritty highway underpass that has become a shrine with flowers, candles and prayers.

The image, which highway engineers said was probably formed by leaking water and winter road salt from the highway above, first began drawing visitors last week. Their numbers grew daily, causing traffic tie-ups in the vicinity and police later blocked-off part of the area.

Some visitors said the yellow, white and gray mark resembles Mexico’s Virgin of Guadalupe, a figure popular in the neighborhood northwest of downtown Chicago where the Kennedy Expressway crosses Fullerton Avenue.

“It’s a miracle,” said one woman, claiming she could see the face of the woman many Christians revere as the mother of Jesus Christ. Some knelt in prayer, others touched the image on the wall and many took pictures using cellular phones.

The Virgin of Guadalupe has been venerated by successive generations of devout Mexicans since she is said to have first appeared to a shepherd in 1531. She is generally depicted in a gown fringed by rays of light.

Highway officials said they planned to leave the wall as it is.