The alleys of Sarajevo’s old city, once an Ottoman-era central market, are crammed with vendors plying their ancestral trades. Mensur Zlatar, whose surname means goldsmith, has a miniscule shop tucked next to the grand Gazi Husrev-beg mosque, named for the Ottoman high-ranking officer who developed the metropolis in the 16th century. Across the street, a clock tower with unusual symbols covering its face rises above the city.

Most days Zlatar can be found mending broken jewelry and watches beneath a faint pillar of cigarette smoke. But the 71-year-old has a second life. For half a century, he has been the keeper of Sarajevo’s prayer time, a posting with the title muvekit. Twice a week since 1967, Zlatar has climbed the 76-step tower of Sahat-Kula, thought to be the world’s only public lunar clock, to set the time.

He adjusts the mechanism on the clock’s four faces for the five daily prayers required by Islam. The time is set according to that day’s sunset, when its hand must be firmly on 12. Without a manual reset, the clock would stop functioning within a week.

The cathedral, mosque, and synagogue that inhabit Sarajevo’s downtown speak to the city’s diverse religious history. In the surrounding winding alleys east and west converge as grand Austro-Hungarian buildings loom over narrow Ottoman-era alleyways.

But this calm unity masks a bloody history. In the 1990s during the dissolution of Yugoslavia, Sarajevo fell under siege for 1,425 days, the longest siege of a capital city in modern warfare history. Even as Sarajevo was surrounded by snipers picking off civilians who dared to leave their houses, Zlatar climbed the steps of Sahat-Kula to set the time every week. He shaved only one visit off his routine, and since the war ended, Zlatar has resumed his twice-weekly climb.

The clock tower was built in the 16th century, and the current clockface was inserted 300 years later, according to Behija Zlatar, the former head of the Oriental Institute of Sarajevo, and Zlatar’s sister-in-law. In 1876, after the original clockface was broken, the current one was inserted into the tower and the first written evidence of a muvekit appears in records.

Since then, five muvekits have held the job, which includes a symbolic salary. Zlatar’s grandfather was one, and occasionally his father helped. As a teenager, Zlatar began his training, and when his predecessor died, he took over. “At that time the muvekit was a big person,” says the silver-haired timekeeper. Since WWII, only he and his predecessor have served as the clock’s caretakers.

“While I am healthy I will continue to do this task,” Zlatar writes in an email. But he hopes to retire after a half-century of service. He tried training his son to take over, but he doesn’t live nearby. Instead, the administrator of Gazi Husrev-beg recommended one of the mosque’s young employees to follow in Zlatar’s footsteps up the 76 steps. When he retires, this young man will take over the time-honored tradition.