You see them all over town, and in the surrounding countryside on both sides of the border. Their numbers are growing, and they've been here for over two hundred years. They are one of the visible traditions that tie us to our past.

What are they? Roadside death markers.

Small piles of rocks can be seen beside the ancient trails that can still be followed in this desert country. We assume they are shrines or offerings of some sort but their exact significance must remain a mystery.

However, the custom of planting a cross at the site of a sudden death came with the Spaniards. The message is simple: This is where someone died without the preparation afforded by the Catholic Church. If you wish, you may pray for his or her soul.

That the custom was well established in our region, we know from a 1783 letter from an official in the Sonoran colonial government, quoting a conversation with Fray Antonio de los Reyes, the first bishop of Sonora.

The good bishop was concerned about the custom of planting a cross wherever a traveler had been killed by the Apaches. It cheapened the holy symbol of the cross, he said, and even exposed it to acts of irreverence. Furthermore it so frightened travelers that they might be too terrified to defend themselves in case of a real attack. Finally, it would only encourage the Apaches to further depredations.

For these reasons, Bishop Reyes asked the authorities to remove all the crosses and order that no further markers be erected. This was duly accomplished.

As we can see today, it didn’t work.

Nowadays the internal combustion engine has replaced Apache warriors as the primary cause of roadside death, but the crosses are still here. There was even a time in the 1950s that they were erected by the Arizona Highway Department as a warning strategy for motorists. However, the crosses we see nowadays are usually placed by grieving friends and relatives . . . I suspect as a way of doing something to ease the pain of loss.

The latest manifestation of this old, old custom may be found in the “ghost bikes” placed by members of the cycling community to commemorate the traffic death of a fellow bike rider. These stark reminders are painted white and equipped with the name and dates of the deceased. Flowers are often placed nearby on the ground. I drove past a ghost bike today at the southeast corner of Mission Road and Irvington.

But be they bikes, crosses, or some other symbol, these public reminders of tragedy seem to be meaningful to an increasing number of people here in our desert.