Once a collection of scattered ruins poking through the jungle canopy in Cambodia, Angkor is now an archaeological park where, beyond a broad causeway, rise the towers of what is probably the world's largest religious building. Known as Angkor Temple or Angkor Wat, it was built by the 12th-century Khmer king Suryavarman II and houses one of his most spectacular legacies: the massive "Churning of the Sea of Milk" bas-relief, which stands apart for the quality of its carving, ingenious composition and the impressive measures conservators have taken to ensure its longevity.
The relief depicts an ancient Indian story. Lord Vishnu cajoles demons (asuras) and gods (devas) into working together to produce an elixir of immortality they both covet. They churn the waters of the cosmic ocean using a sacred mountain as a pivot and a supernatural, five-headed snake as a rope. Lined up on either side, asuras and devas take turns pulling, causing the mountain to swivel back and forth, stirring the waters. When the mountain suddenly begins to sink, Lord Vishnu keeps it afloat till their churning produces the elixir. (Vishnu later nabs the elixir to prevent its misuse.)
The "Churning" was a popular motif, and the carvings on lintels and pediments at Angkor help us see the choices involved in tackling a 12-by-159-foot relief. In smaller formats, artists typically created dynamic, balanced compositions by depicting asuras and devas mirroring each other as though competing in a tug of war instead of coordinating a seesaw action. But for this monumental relief—set in a narrow and elevated colonnade that forces viewers to walk alongside the carving, never getting more than a partial view—Suryavarman's artists tweaked this symmetrical composition, managing to align it more closely with the divine epic while pumping up the drama.
By the time you reach the "Churning" you have seen a profusion of carvings depicting Hindu deities inside rich foliated patterns, kings and gods leading processions and waging battles, and near life-size heavenly maidens—apsaras—slim-waisted and bejeweled. The "Churning" at first seems more of the same. Laid out in three registers, the initial scenes at both extremities teem with infantrymen and soldiers, horse-drawn chariots and elephants. Though the carving, probably originally painted, is shallow, artists imparted depth by layering and overlapping horses and soldiers.
Then, like the vertical lines separating drawings in a comic strip, towering figures rise up holding the head or tail of the snake. From then on, the lower register sports a swirl of crocodiles and fish balanced by heavenly apsaras in the upper register. Long lines of asuras and devas punctuated by giant leaders fill the large middle register with lively, syncopated rhythms.
Walking with the relief on your left, 91 asuras line up in a succession of arms arcing forward, bent knees pointing back like arrowheads, and, beneath a play of overlapping legs, splayed feet pointing in opposite directions, reiterating the tension of the story's action. It is a wonderful use of repetition and line, made all the more menacing by the asuras' tense bellies and popping eyes. Even when you walk in the opposite direction, there is no escaping the feeling that the dark side is dragging the good guys down. The devas are slightly fewer in number and their arms and knees point toward the asuras. An inexorable momentum favors the demons.
This is realistic. When it is the asuras' turn to tug, devas should be giving way. But this is also symbolic, fueling the fear of neighboring enemies and casting Suryavarman II as save-the-day Vishnu—all of which brings us to the center of the relief. Vishnu forms the central axis, appearing both as a tortoise lifting the mountain and as a four-armed god wielding weapons and adding divine muscle to the cosmic push-pull. To express just how strong the churning is here, artists carved the fish broken into pieces and flung about in disarray. This may echo the artists' own fate in the wake of Suryavarman's final military defeat. They left the mountain incomplete and, though they carved the lovely apsaras that emerged from this creative stirring, there is an unfinished patch where the elixir would normally appear.
By tracking how sunlight moves across the carving and finding numerical correlations between the composition and astronomy, one scholar argues that the "Churning" doubled as a solar calendar. Others show the relief fitting into a scheme aimed at promoting sacredness and kingship, while legitimizing Suryavarman's usurpation of the throne.
As research continues, so do preservation efforts. Early this year, the New York-based World Monuments Fund (WMF) rebuilt the colonnade's roof, a four-year project that involved dismantling an earlier reconstruction made before everyone realized how much salts in cement damage stone. Through trial, error and myriad consultations with experts, the Cambodian WMF team discovered that the 12th-century builders had notched the roof's massive sandstone blocks, then pitched them to promote drainage. Senior architect Cheam Phally beams as she explains the ingenuity of her forefathers, keen now to understand what exactly fit into holes discovered on the roof's capstones. She knows even stones cannot live forever; still, she hopes her efforts have helped extend the life of Angkor Wat's prized relief. After all, she says, "there is no other like it."
—Ms. Lawrence is a writer based in Brooklyn, N.Y.