Celebrated since the fourth century, the Christian tradition of All Saints' Day is observed each year Nov. 1. Less well-known than the secular traditions of Halloween, such as carving pumpkins and trick-or-treating, All Saints' Day holds deep spiritual importance among many Roman Catholics.

The first All Saints' Day was celebrated when Pope Boniface IV collected bones and other remnants of saints and reburied them in the Pantheon in Rome, according to the American Catholic newsletter. The pontiff's gesture grew into a broader practice that led believers to gather at the burial places of Christians who had been considered martyrs and reflect on their lives on the anniversaries of their deaths.

As more saints were canonized over the years, Pope Gregory IV later decided to designate one day of the year to celebrate them all, choosing Nov. 1. There are more than 800 canonized Catholic saints in 2015.

In many churches throughout the world, the practice of commemorating dead saints has expanded to include the remembrance of regular churchgoers. In many parishes, priests gather the names of dead parishioners and their loved ones for inclusion on a list to be read during Mass on All Saints' Day.

The day is celebrated in slightly different variations throughout the world. For instance, some Christians in Sweden observe the day by lighting candles by the graves of their loved ones. Other Christians there lay flowering heather and wreathes.

"It's a way of remembering previous generations. It's acknowledging our ancestry in faith, all the baptized, those who lived before us," said one Alabama priest, adding "They are saying that person is still with us. That's the Christian belief. When the body dies, we don't die. We are still present."