MONTGOMERY, Ala. (AP) — If these singers were in a sanctuary or on the church grounds, you’d think you were at an old-time revival.

But these voices, distinct in tune but united in harmony, are singing shape-note music, a sacred form of choral music that dates back more than two centuries. Once an almost forgotten folk tradition, shape-note singing is gaining new fans, young and old, in America and around the world.

And they’re not in a church — this group of about 70 fills an auditorium at Old Alabama Town for a regular gathering of the Capitol City Shape Note Singers. It’s an all-day event sponsored by the Landmarks Foundation and the Alabama Center for Traditional Culture.

To a passer-by who’s never heard this music, the songs have an energy; some resemble chanting, with an almost haunting quality. Some almost seem like shouting. The lyrics are often taken from old hymn texts, some dating to the 1800s, with titles that evoke a sense of old-time religion: “Vale of Sorrow,” ”When the Lord Shall Come for Me,” ”The Rock That is Higher Than I.” Themes of redemption, salvation and eternal peace are common, but so are cries of “hallelujah.”

But though it is a spiritual form of music, it is non-denominational; many of these singers became acquainted with shape-note through church singings, but it has a secular component to its past.

“Most of these singers, when they go to a singing, they’re not going to a church service,” said Joey Brackner, director of folklife projects for the Alabama State Council on the Arts and a participant in this singing. “They’re just going to a singing. That’s why you’ll hear people refer to this as the ‘class,’ and the ‘leader,’ and the songs as ‘lessons.’ Because this whole tradition came out of teaching music.”

“Shape note” refers to the musical notation that uses note heads in four distinct shapes; each of the four shapes is connected to a particular syllable, fa, sol, la, or mi. The shape for fa is a triangle, sol an oval, la a rectangle, and mi a diamond.

The shapes help those who can’t read music to identify the notes on a musical scale. The term “sacred harp,” which shape note is sometimes called, comes from the title of the shape-note songbooks from which the music is sung.

Pitch is not absolute, as there are no instruments. The leader — this task rotates among all singers who wish to call out a song number and lead it — finds a good pitch and intones it to the group. The singers reply with the opening notes of their own parts.

This is not a performance; rather, it’s a participatory event, where the singers are singing for themselves, not an audience. The curious are welcome to listen and observe, but they’re also encouraged to grab a book and become a part of this joyful wall of sound.

“The sound is awesome, and it’s different. This is like early America. There’s no musical instruments, but everybody is singing out. With gusto. There’s no bashful singing to it,” said Stanley Smith of Ozark, who’s been singing shape-note music for more than 40 years now. He also is a composer, with several songs in one of the books used at the Old Alabama Town event.

“I had one come to me just a couple of months ago. It’s unexpected. Don’t know when it’s going to hit, but when the Lord sends it is what we go with.”

Many of these singers are from Alabama, but some are from other states; Rebecca Over, one of the alto singers, is visiting from England for two months to attend singings around the South.

She said shape-note singing has been in the United Kingdom since at least the mid-1990s, and there are now groups across Europe — in Germany, Poland and Ireland.

For her, the appeal of shape note is the singing. “It really deeply moves me. It’s a form of worship. The harmonies are very special, because each of the four parts has its own tune.”

Most singers appreciate that this music is a tie to history, an oral tradition that links them with generations past. Though the lyrics are old, the words transcend time.

“It’s the tie in to so many generations that have experienced the same things that we’re singing about,” said Mary Amelia Taylor, who came to the singing with her dad, Tim Taylor, and his fellow church member, Elizabeth Duffy. All three are from Monroe County.

The genre has its roots in New England in colonial times, and it spread south and westward in the early 19th century. The form began to die out in the Northeast prior to the Civil War, but took hold in the rural South, where perhaps because of isolation, the tradition continued to the present day.

The tradition likely got a boost from the 2003 Civil War-era movie “Cold Mountain,” starring Jude Law and Nicole Kidman. But for those who sing it — some of whom travel hundreds of miles to attend regular singings — whether or not it has a presence in the mainstream is not important.

For them, the power of this music is evident in the “hollow square” — the shape formed by the seating arrangement of the singers, which is always consistent regardless of the location of the singing. The four parts — treble, alto, tenor and bass — sit on the side assigned to the part, facing inward. In the center of the “hollow square” is the leader, who calls the song, gives the pitch and moves his or her arm to keep time.

To be in the leader’s position, in the middle of the square, is one of the benefits of leading. With sounds coming from all four direction, the sonic experience is impressive.

“Once you experience it — if you stand in the middle, and that sound is coming at you from all sides, it’s really powerful,” said Mary Amelia Taylor. “And it’s incredibly addictive.”