The reason for their constant transformation, he explained, is not the assaults of wind or water, which never seem to trouble the neatly interlocking rocks. Someone keeps knocking them over — eight times, so far, in just seven weeks. And Mr. Gryka keeps reassembling them into new forms.
He had arrived that morning at 11:30 by bicycle from his apartment in North Riverdale, the Bronx, to find the entire collection — a week’s effort — pulled down.
“I was angry,” he said. “They must have been big people to be able to move these rocks. They pushed over every single one, even the big, heavy bases.”
Then he slipped his earbuds back in and got to work. Three hours later he had finished a new cluster of towers — more than 35 in all. By week’s end, there were close to 100.
“When I started out, it was a small, shy exhibition,” Mr. Gryka said. ”But it’s grown larger with each destruction. This has been a very perseverant work.”
Many of the people who stop to marvel liken his figures to cairns, piles of rock that have turned up around the world since prehistoric times to mark pathways, honor deities or commemorate the dead. (In fact, the monumental, mosaic-covered “Hell Gate Cairns,” by the artist Samantha Holmes, were installed along the Hudson near 66th Street after Mr. Gryka began; he learned of them only last week.) Others mention modern environmental artists, like Andy Goldsworthy, who create outdoors, using natural materials at hand.
“Goldsworthy, Noguchi, Giacometti,” Mr. Gryka rattled off the names his visitors drop. “I want to be extremely honest: I didn’t know who these people were until I went and Googled them.”
He thanks search engines and childhood earth-science classes for an acquaintance with his materials. “Manhattan schist, composite rock, quartz,” he said. “There’s some granite over there.”
But Mr. Gryka’s real passion is the personalities he discovers once he has combined stones into a single statue. “All of them have something different, something particular. I can see traits.”
He pointed out a warrior and a mariner. Although he sometimes calls them the stone men, there are women, too: one with wide shoulders that suggested a shawl, and a seated Madonna holding a child. At the front of the group, he always erects a figure, taller than the others, that he calls “the high priestess.”
“She’s like a leader conducting the orchestra, and all are looking to her,” he said. “They are like a hive of bees — they need a queen.”
His father, a surveyor for bridge and building projects, kept beehives as a hobby before the family fled Albania’s civil unrest in the mid-1990s for Italy. Mr. Gryka, who speaks four languages, studied political science at the University of Milan, then came to the United States in 2007 with a green card he obtained in a visa lottery.
In New York, he became a United States citizen and earned a master’s degree in international affairs from the New School, but jobs in his field, conflict and security, have not been easy to come by. He worked as a server in restaurants, then quit in April to take a break from the stress and restart his job search.
On his daily runs down the river path, he began to notice the jagged stones along the shore. “I came here to clear my mind and figure out where I am going,” said Mr. Gryka, who follows the teachings of Sufism, a mystical branch of Islam. “I started to move the rocks as a sort of healing practice.”
He made some stacks farther south, but soon came to favor the spot by the bridge, in Fort Washington Park, drawn in part by a fascination (fitting for someone named Ulysses) with borders and water crossings. One night, his darkened parade of silhouettes struck him as an image from Dante — “all the souls waiting on the Styx River for a boat to take them to the other side,” he said.
He toils on the site most days for at least a few hours, his earbuds piping a stream of Sufi chants.
Each new figure begins with a face. “First I find what looks like a head,” he said. “Then a hat. Every head needs a hat.” (Five minutes later, he spotted a man placing a pebble on top of a finished piece. “Someone added a hat!” Mr. Gryka exulted. “Good work.”)
Then he looks for a base and other parts, using sight, feel and instinct to find surfaces that will fit together. “You work with what’s around you. You study the top edge, and look for a rock that matches. It’s like a puzzle.”
On Sunday, Jessica Woods and her 8-year-old daughter, Aine, made a pilgrimage from their apartment at 148th Street and Riverside Drive, after a neighbor told them about the stones. Ms. Woods called out to Mr. Gryka: “Thank you! We’re so grateful to you for this.”
“They’re magical — the patience and balance,” she added. “And then there’s the grace with which he’s handling how his creations were pushed over by vandals.”
Mr. Gryka is not the first freelancer inspired by the Hudson waterfront, or besieged by forceful critics. A decade ago, one man used boulders to anchor huge sculptures he fashioned from scavenged driftwood, only to see them removed by workers from the city’s parks department.
The damage to Mr. Gryka’s pieces hasn’t all come at the hands of strangers. On Labor Day, he dismantled his figures after a Parks Department employee warned him that they could topple onto someone, and ordered him to take them down. The next day, Mr. Gryka says, he sought out a parks crew, hoping to apologize; one told him that he had done nothing wrong and that he should rebuild. (The department did not respond to questions about its policy on such matters.)
Mr. Gryka is not sure how long he’ll keep at it — maybe another few weeks or a month, when colder weather sets in. Even the labors of Sisyphus must end sometime.
But the rocks have lives of their own that will go on, Mr. Gryka said, reciting a verse by the 13th-century Sufi poet Rumi:
A stone I died and rose again a plant;
A plant I died and rose an animal;
I died an animal and was born a man.
Why should I fear? What have I lost by death?