More than 500 years old, Santa Croce also sanctifies the tombs of Michelangelo and Galileo, two men famous for the marks they left on the Catholic Church. The battered, dark blue and red cross hanging in one of the small chapels near the sanctuary was the shape of Christ, still visible on its painted surface despite water damage. The sanctuary is a physical structure full of religious symbols. But those who see it or worship in it know that it is also made up of special behaviors, such as silent contemplation or the ritual of communion. Visitors to places like Santa Croce have rules to follow because sanctity is created and maintained, at least in part, by the boundaries we place around it.
“Religion seems to be based on separating the sacred from the profane,” said Father Terrance Klein, pastor of St. Joseph Catholic Church in Ellinwood, Kansas.

The boundaries governing sacred spaces, whether limiting entry or enforcing silence, may seem arbitrary, but according to Rev. Klein and others who have studied the concept of sacredness, they are deeply connected to how people of faith understand their relationship with the divine. They take us out of the chaos of everyday life and push us into a deeper connection with God and with each other.
“There is a human need to know when you encounter God. Every religious group, in some way, says it's because you stepped into a certain space or because it's this time of day,” said Rev. Klein.
The power of this encounter is not lost when outsiders come in. It can also convert tourists, even if they've only stopped to admire the architecture of a sanctuary, says the Rev. Rose Duncan, canon of worship at Washington National Cathedral.
“When people come to visit, they may see (the cathedral) as a place almost like a museum. But what happens is that they have the opportunity to be invited inside to worship.”

What is sacred?
Some of the world's most famous holy places, such as the Temple Mount in Jerusalem or St. Peter's Basilica in Rome, have become important spiritual sites because of people's beliefs about what happened there in the past.
“What makes a place sacred is that, at least in the beginning, the gods manifested themselves there,” says Richard Hecht, professor of religious studies at the University of California, Santa Barbara. He cited Ayers Rock in Australia as an example, where indigenous tribes believe their gods manifested themselves.
Most churches, synagogues, temples and other places, including mosques, are sacred because of what is happening inside them today. God is invited in through prayer, song and other rituals.
The Rev. Klein, former professor of theology at Fordham University, said separation from the secular world is a fundamental part of holiness. When people cross the threshold of a house of worship, they are expected to feel and behave differently.
This separation, he said, is a way of saying, “We are now in the presence of God.”
Our understanding of appropriate separation can evolve over time. For example, before the Second Vatican Council of the Roman Catholic Church in the 1960s, “the sacred was so sacred that only clergy could witness what was happening at the altar,” Fr. Klein noted. Vatican II broke down some of the barriers between clergy and laity.
Most religions, including Christianity, Islam and Judaism, teach that worship need not be confined to a church or chapel, but setting aside a sacred space allows these traditions to create a place where people can consciously connect with the divine, Father Klein added.
“These religions say that God is everywhere. But they also ask, 'How do we focus our attention?' They do that with sacred space,” he said.

Why are borders important?
Walking through St. Peter's Basilica with hundreds of tourists in September, a stern-looking young man looked up at me from his post near the entrance to the Blessed Sacrament Chapel. His task was to separate the true worshippers from the other Basilica guests so that only members of the old group could have access to the space.
I squeezed outside the wooden partitions set a few meters away from the chapel entrance and squinted to see the chapel's altar decorated with golden angels and lapis lazuli accents.
Fr. Klein, who led services at St. Peter's as a theology student in Rome, said boundaries like the chapel guard are about practicality and maintaining sanctity.
“There are so many people coming in and out. They try to reserve space for people who are just there to pray,” he said.
Other measures ensure that visitors do not knowingly or unknowingly mock one of the church's rituals. For example, Father Klein is supposed to put communion wafers on people's tongues, not in their hands, during worship services at St. Peter's.
“We don't want the Blessed Sacrament to be in a photo album,” he said.
Visitors to the basilica are kept away from the main altar and confessional with velvet ropes. The space under the church dome, large enough for the Statue of Liberty to stand, is empty on one side of these barriers and overrun on the other. People push each other to get the best camera angle and miss the tour groups.
Limitations like these ropes made me worry about the impression I was making on truly devout pilgrims or people who felt compelled to visit St. Peter's because of their commitment to Catholicism. As I hurriedly transcribed my tour guide's facts and took photographs, these spiritual tourists made their way to the statue of St. Peter, kissing or touching his metal foot, having done the same by thousands of other pilgrims.
I saw the sorrowful look on a woman's face when she tried to leave roses at the tomb of St. John Paul II and the guard told her she was not allowed. I saw people content to look around and soak in the marble columns and high arches, while I wondered which statues were worth photographing. I was humbled by the devotion shown while worrying about the mundane.
Hecht noted that my dual reactions were a natural reaction to sacred space. The boundaries around them are as much about who they keep out as who they let in.
“Your ability to control access to a place is perhaps the most important part of sanctity,” he said.
In the Church of Jesus Christ of Latter-day Saints, only those with a recommend can enter the temple after dedication. In some Catholic churches, the unbaptized and unconfirmed are asked to leave the sanctuary before communion.
Hecht added that such strict boundaries can strengthen the bonds between those who are admitted, noting that setting boundaries around a sacred space is “an effort to create a community.”
In addition, transgressing restrictive boundaries can be more meaningful. When we create boundaries consciously and know why they are there, “they can be powerful,” said Fr. Klein.

Transcending division
Because of the important role that borders play in sustaining religious communities, it can be surprising to see how many faith groups are willing to allow people to cross them. But allowing tourists to see St. Peter's Basilica or allowing community members to visit a newly built Mormon temple can bridge religious differences and invite people into a deeper relationship with the divine, Reverend Duncan said.
In August and early September, 141,000 people, including 70,000 non-Mormons, walked through the newly built Philadelphia Pennsylvania Temple. Secular media outlets such as Religion News Service reported on the open house, raising awareness about the design and purpose of the temple before it was closed to outsiders for the dedication ceremony on September 18.

A group of visitors line up to tour the Philadelphia Pennsylvania Temple of the Church of Jesus Christ of Latter-day Saints in Philadelphia, Pennsylvania, on August 10, 2016. | Alan Murray
Open house guests see a temple's immaculate living rooms, chandeliers and spaces where brides and grooms prepare for their sealing ceremony. They are also invited into the “heavenly chamber”, seeing how bright lights and ornate fixtures welcome those seeking the last few moments of peace and quiet before returning to the outside world.
Sacred spaces are often incredibly beautiful places, and the people who run them take this into account when deciding to share them with outsiders, Rev. Klein said.

“Even a person who doesn't believe in God at all should be able to see St. Peter's. It is, if nothing else, a triumph of the human spirit,” he said.
And the tourist-like interest is not limited to the famous churches of Rome and Florence. According to a new study of what religious groups contribute to American society, nearly 117,000 US parishes report that visitors come to their places of worship just to see the building and the artwork.
The Rev. Duncan, who oversees worship at the National Cathedral in Washington, D.C., said he is not concerned about the tens of thousands of non-Episcopalians who flock to the cathedral each year.

“In my mind, there is always an opportunity for someone to experience God here,” he said. “We just want (visitors) to respect that during the time that people are worshipping and preserve the sacred nature of our time together.”
Tourists may leave their visit with a few pictures and historical facts about the place, or they may be spiritually changed. Rev. Duncan recently heard of a visitor to the National Cathedral who learned of his uncle's death during the tour.
“They thought they would be here for 30 minutes and they spent three hours,” he said. “They felt that God was with them.”

Divine Benefits
As Fr. Duncan's story shows, holy places offer solace to people in pain or mourning. They also offer other, more subtle benefits to the tourists who are allowed inside, as I learned on my recent visit to the National Cathedral.
I reached the entrance to the church by navigating an obstacle course of playgrounds. Dozens of girls, dressed in purple and yellow, ranging in age from 6 to 18, were throwing balls at each other, screaming, smiling and basking in the sun.
By comparison, the cathedral was quiet and shadowy. Illicit whispers could be heard among the guests and the cries of a distant baby, but it was shocking that the noise from the lawn outside into the main worship space had diminished. My mouth may have hung open in astonishment.
The long aisle of the cathedral's main sanctuary, speckled with blue and purple light streaming in through stained glass windows, was visually spectacular. I no longer cared how sticky I was from a long, sweaty walk because I was so grateful to have had time for this space on my short trip to the country's capital.
Hecht said it is relatively common for the boundary between the sacred and the mundane to be defined by a change in noise level. “I think it's part of responding to the sense of awe of a sacred place. You have to be quiet.”
I was aware of this fact, but I was still overwhelmed as I walked down the main aisle of the National Cathedral. Sacred spaces are hard to get used to, no matter how many times you visit them.
Inside the cathedral, a worship service was beginning. I sat on a hard, wooden pew and listened to a sermon about attracting people to religious practices at a time when many people are leaving religion. I put my phone away and tried not to think about how long it would take me to get back to my hotel.
Time slows down when you are in a place like the National Cathedral. The stained glass windows, statues and stonework cry out to be noticed, but only worship leaders and a few random tourists can be heard.
The sanctuary offers a sense of calm to counter the storm of modern life. It invites people to reflect on art and architecture, spirituality and theology, distracting them from smartphone notifications and social media.
As I stood up and walked towards the door, walking towards the crying baby and excited schoolgirls, I heard one of the last moments of the service being broadcast over the cathedral's loudspeakers.
“The Lord be with you,” the priest said.