PRAGUE — With its soaring Gothic cathedrals and ancient alleyways lined with baroque architectural marvels spread beneath a majestic castle that overlooks the city, Prague can seem a place frozen in time.
But for more than 600 years, one clock has been measuring the passing hours, noting when day turns to night as well as the position of the sun, moon and stars.
Until last week.
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Prague’s famed Astronomical Clock, the Orloj, in the city’s Old Town, has been stopped for repairs.
It is not the first time it has been stopped, but every intervention is fraught, given the clock’s age and fragility. And this one is the most ambitious in years. So for Prague’s clock master, Petr Skala, it is a little like being a surgeon at work on a very old patient.
Mr. Skala has until the end of August to complete a major renovation of the Orloj, one of the oldest clocks in the world.
When he is done, the engineering marvel that started ticking in 1410 will have been returned to its medieval roots in ways both visible and invisible to the crowds that assemble daily on the square below. In an effort to be true to the original clock master’s design, he will, in effect, have turned back time.
Mr. Skala, 71, plans to replace some of the more modern metal gears that turn the intricate machinery of the clock with a wooden system modeled on the original design.
On the exterior, the colors on the clock’s face will be tweaked to restore their original shading, and several of the sculptures that adorn the tower will once again represent the best and worst of human traits: pride, envy and avarice paired with compassion, generosity and humility.
Evincing the last of those virtues, Mr. Skala said humbly that he was simply working to “remove inappropriate and removable adjustments and return the clock to its original look.”
A sculptor by trade, Mr. Skala has long been fascinated by clocks — for both mechanical and romantic reasons. “A clock measures time,” he said. “And time is the most precious gift we are given.”
As a child, he said, he would remove the clocks from the walls of his home to take them apart and probe how it was possible to measure the passage of time.
“I love history,” he said on Monday after climbing a set of narrow, winding stone steps to reach the tiny nook that houses the guts of the machine in the tower of the city’s old Town Hall.
Workers disassembled the timepiece as he spoke, and Mr. Skala later loaded some of the precious cargo into his beat-up, old hatchback parked on the street below to be taken to his studio.
From the first clock to the Apple Watch, measuring time has been central to human ingenuity. “The whole development of technology is written in the clock,” Mr. Skala said.
Perhaps no other clock better demonstrates the genius of the early pioneers of time keeping than the Orloj. Marking the minutes and hours is only one of the many measurements it provides.
It tracks Old Bohemian time, when the new day began with sunset; Babylonian time, which tracks the day from sunrise to sunset; Central European time, which is marked with a distinctive hand in the shape of the sun; and Star time, measured by the way the stars appear to move because of the Earth’s rotation.
A calendar dial notes the days of the week, month and year, and a zodiacal ring shows the path of the sun and moon through the sky.
But it is the astrolabe that is the heart of the clock’s mechanical operation. The apparatus, which tracks the position of the sun, moon and stars, has been an essential tool for astronomers and mariners dating back to antiquity.
Mr. Skala, who has been a certified clock master for 25 years, said he was honored when asked to take care of the Orloj eight years ago. He is responsible for several other well-known clocks around the city, including the one at St. Vitus Cathedral at Prague Castle. But none compare to the one at the old Town Hall.
“This is where Czech history happened,” he said from the clock tower, pointing to the nearby memorial to John Hus, who was burned at the stake for his beliefs and whose death set off the 15th-century Hussite Wars.
“The clock just keeps ticking,” Mr. Skala said.
Over the centuries, it has been modified, damaged and repaired — but always returned to fully working order, even after taking a fusillade from German soldiers in World War II.
Its longevity has inspired a number of myths surrounding its operation, including at least one that predicts doom: When the clock stops running, the legend goes, the Czech land will be thrown into war and privation.
Another legend holds that whoever tries to affect the machine will die or go insane.
Asked whether he gave such legends any credence, Mr. Skala smiled.
“I cannot believe the stories,” he said, “or else I would never be able to work on the clock.”
