From his stone balcony, Dan Tirza looks out over a rippling expanse of Judean desert, the biblical landscape of the Jewish people. A student of that history, the retired army colonel is a leading actor in Israel's modern story of statehood, conquest and the volatile task of erecting a boundary that divides Arab from Jew.

Soon Israel's $2.5 billion separation barrier will rise around Tirza's settlement, where 350 Jewish families live among palms, playgrounds and a synagogue 10 miles inside the West Bank.

The Israeli government says it is building the 456-mile barrier to protect its citizens from Palestinian attacks and not to establish a border. But the route does not follow the boundary defined when Israel emerged as a modern state in the late 1940s, drawing complaints from Palestinians that the barrier's path is designed to seize land and dictate the terms of a future peace deal.

Tirza's settlement is among dozens of hilltop redoubts that Israel has built over the past generation, creating a mosaic of Jewish communities in the Palestinian territories. When the barrier is complete here, it will place on Israel's side nearly 25 square miles of the West Bank, the proposed heartland of a future Palestinian state.

Tirza supports the route in no small part because he, more than anyone else, drew it.

"The main thing the government told me in giving me the job was to include as many Israelis inside the fence and leave as many Palestinians outside," Tirza said in an interview. "The idea was to do it with balance."

Tirza, a Jewish settler who believes Israel has a historic right to the land between the Mediterranean Sea and the Jordan River, drew the barrier along a route that effectively annexes 10 percent of the West Bank. In the absence of a peace agreement, the course cements the territorial claims of tens of thousands of Jewish settlers, including Tirza's.

Recently retired after three decades in Israel's army, Tirza has had to defend his design in court, been accused by dovish Israelis of having a conflict of interest because he lives in a West Bank settlement, and antagonized neighbors who oppose the project because it divides what they see as Jewish territory.

His design highlights Israel's twin and often conflicting goals: ensuring the security of its citizens while solidifying its hold on land the Palestinians envision as part of their future state.

"He's a bit of a enigma, but I've always had the impression he was more motivated by ideology than by power or money," said Michael Sfard, an Israeli human rights lawyer who has challenged the barrier's route and confronted Tirza in court several times. "That might sound like a compliment. But in the job he was supposed to do, he tried to mask his ideology and present it as a concern for security."

Tirza is 48, an older-than-usual doctoral candidate who favors jeans, Teva sandals and wraparound sunglasses to go with the knit skullcap favored by religious settlers. His short, black hair is receding.

The son of secular parents, Tirza joined the army in 1977. As a young lieutenant in the early 1980s, Tirza served in the Nahal, a select unit the Israeli Defense Ministry used to establish what would become civilian settlements in the territories Israel occupied during the 1967 Middle East war. The defense minister at the time was Ariel Sharon, with whom Tirza would work closely on the barrier two decades later.

"One day he took me in a helicopter and set me down in a spot in the desert," Tirza said of a trip he made in the early 1980s. "He told me, 'This is where you will settle.' " Tirza did make his home in the southern West Bank, not far from the spot Sharon had indicated.

In March 2002, as scores of Israelis were being killed in attacks during the second Palestinian uprising, the Likud-led government of then-Prime Minister Sharon resurrected the idea of building a barrier, which had been proposed six years earlier by the rival Labor Party.

"The army had asked for it, and the government said no because of money," Tirza said. "But the real reason was that no one wanted to draw the line."

When he was given the job of designing the barrier that summer, Tirza was known as the officer who knew the West Bank's topography more intimately than anyone.

Sharon's security cabinet approved the barrier's first three segments in June 2002, a year when the number of Palestinian suicide attacks peaked at 60.

Last year, according to Israel's Foreign Ministry, there were five. But some Israeli military officials say factors besides the barrier -- including stepped-up army operations in the West Bank and a two-year-old decision by most armed Palestinian factions to refrain from such attacks -- better explain the sharp decline.

Working from an office in the army's Central Command, Tirza headed a staff of 36 people from the army, police agencies, the environment ministry, and the military government in the territories. The group pored over maps, considered water rights and archaeological sites, and began the task of facing angry Palestinians as cement and chain-link cut into their land.

"There is always going to be a man behind the fence," Tirza said. "The Palestinians need us. And we need them to be good neighbors."

During several hours of touring the barrier recently, Tirza described what he said was a painstaking process of working with Palestinians to find the best course. But the visits also illustrated the hardships imposed on them by the barrier's circuitous route through the West Bank.

Highway 443

Highway 443 runs northwest from Jerusalem toward Tel Aviv, a shortcut of crests and valleys through the West Bank.

But only Israelis and a relatively small number of Palestinians with permits are allowed to use the four-lane highway, part of a separate road network Tirza conceived, also in the name of Israel's security. The narrow roads that once connected 443 to dozens of Palestinian villages have been sealed off with cement blocks and berms.

In June, Israel's high court ordered the government to explain within two months why Palestinians are barred from the highway, an inconvenience that has made classrooms, hospitals and jobs more remote for thousands of them.

North of Jerusalem, the highway runs between At-Tira and Beit Ur Al-Fauqa, a pair of Palestinian villages inside the West Bank whose children attend a small pine-shaded school situated between them.

The school's playground sits in the shadow of the separation barrier. Most of the school's 330 children live in At-Tira and must pass beneath the highway through a tunnel Tirza opened to accommodate them.

"This cost a lot of money," explained Tirza, who said he worked with Palestinians along the barrier's route to find the least disruptive path. "But I tried to minimize the impact."

But Ahmed Abu Bakr, the 55-year-old school principal, said he never met Tirza. "The decisions that affect us are in the hands of the Jews, not our own," he said.

The school's main gate, adjacent to the wall, has been padlocked by Israel's army, which patrols the area to protect a nearby Jewish settlement and Israeli commuters using the highway. Abu Bakr said the children study in fear.

"I feel like I'm surrounded here," he said. "There's no connection between the school and the At-Tira municipality. We're all alone."

Qalqilyah

Farther north, the wall encircles the West Bank city of Qalqilyah and has helped fuel political change at odds with Israel's interests.

Cars enter Qalqilyah through an Israeli checkpoint. The city's farmers must pass through Israeli-operated gates to work their avocado, olive and citrus groves outside the wall.

During the uprising, Qalqilyah served as a transit point for suicide bombers from the northern West Bank. In 2002, the Israeli army kept the city closed for 215 days. Tirza said there have been no closures since the wall was completed around the city nearly three years ago.

By then, the armed Islamic movement Hamas had won many converts in the economically ravaged city, through its charity networks and militant message against Israel. The party won every council seat in the May 2005 municipal elections.

"There is a problem with hatred," Tirza said, as Israeli army jeeps buzzed around the wall's perimeter. "The main problem now with this separation is that they don't know us anymore."

Azariya

Along most of its length, Israel's barrier consists of metal fencing, patrol roads and razor wire, cutting a 150-foot-wide swath through the rural West Bank. But in cramped urban areas -- about 5 percent of the total -- the barrier is a 24-foot-high cement wall that takes up less space and protects against shooting.

In these places, it has become a canvas for protest murals and slogans, including a several-mile segment running from Azariya, a Jerusalem suburb also known as the biblical town of Bethany, south toward Bethlehem. The stretch also carves a confusing course -- incorporating some West Bank neighborhoods on Israel's side, abandoning others previously annexed to the Jewish state -- that illustrates the inconsistent way it was drawn in places.

"Nothing to see here," Tirza said, reading aloud the large block letters in English. He chuckled. In nearby Abu Dis, though, he bristled after reading "Berlin Wall" emblazoned on the gray background.

"That was a political barrier, and this is a security barrier," Tirza said. "That was electrified, there were attack dogs and automated machine guns guarding it."

"But there are some things that are the same," he continued. "The real solution to all of this will come with a peace agreement. And then, especially in Jerusalem, the wall will come down. And I will be among the first to help bring it down."

Tirza said he drew the wall around Jerusalem on a path that did not always follow the municipal boundary, sometimes excluding neighborhoods that Israel annexed after occupying East Jerusalem in the 1967 war. In Azariya, he placed on the Israeli side more than a dozen Christian monasteries that sit outside the Jerusalem city limits after they requested inclusion.

The wall also bisects some Arab neighborhoods, separating thousands of Palestinians from family cemeteries, the nearest hospital and businesses. Yakin Rajabi, a Palestinian carpenter in Abu Dis, lived across the street from his workshop. Now it sits on the far side of the wall.

"It is easier for me to go to Venezuela than to the Damascus Gate," said Salah Ayyad, an Abu Dis city councilman born in Jerusalem's Old City who is now able to visit only with rarely granted Israeli permission. "If they have a wall to separate Arabs from Israelis, fine. But we are Palestinians. Why are they separating us from each other?"

'The Least Bad Line'

In his retirement, Tirza, a father of five, is finishing a dissertation on how private-sector principles can make army units run more efficiently. He gives tours of the barrier to new Israeli ambassadors, helping them prepare to explain it to critical foreign audiences.

He also appears in court to defend his route, despite an order last year from then-Defense Minister Amir Peretz forbidding him to do so. Peretz sought to bar Tirza's testimony after the high court found that Tirza gave misleading reasons for the fence's route around one settlement. He said he has lost only three legal challenges to the path he drew, out of the more than 120 complaints that have been filed against it.

"This is the least bad line I could make," Tirza said. "In every place, there were problems. But I think we have saved the lives of hundreds of Israelis."