So public space, even a modest and chaotic swath of it like Taksim, again reveals itself as fundamentally more powerful than social media, which produce virtual communities. Revolutions happen in the flesh. In Taksim, strangers have discovered one another, their common concerns and collective voice. The power of bodies coming together, at least for the moment, has produced a democratic moment, and given the leadership a dangerous political crisis.

“We have found ourselves,” is how Omer Kanipak, a 41-year-old Turkish architect, put it to me, about the diverse gathering at Gezi Park on the north end of Taksim, where the crowds are concentrated in tent encampments and other makeshift architecture after Mr. Erdogan’s government ordered bulldozers to make way for the mall.

And there’s the hitch. The prime minister has emerged as the strongest leader Turkey has had since Mustafa Kemal Ataturk founded the republic — but he remains not much of an architect or urban planner. Like other longtime rulers, he has assumed the mantle of designer in chief, fiddling over details for giant mosques, planning a massive bridge and canal, devising gated communities in the name of civic renewal and economic development. The goal is a scripted public realm. Taksim, the lively heart of modern Istanbul, has become Mr. Erdogan’s obsession, and perhaps his Achilles’ heel.

And it’s no wonder. Taksim’s very urban fabric — fluid, irregular, open and unpredictable — reflects the area’s historic identity as the heart of modern, multicultural Turkey. This was where poor European immigrants settled during the 19th century. It was a honky-tonk quarter into the 1980s, a haven to gays and lesbians, a locus of nightclubs, foreign movie palaces and French-style covered arcades. Gravestones from an Armenian cemetery at Taksim demolished in 1939 were used to construct stairs at Gezi Park, a republican-era project by the French planner Henri Prost that is like the jumble of high-rise hotels, traffic circles and the now-shuttered opera house on the square, named after Ataturk. It is a symbol of modernity.

The prime minister’s vision of a big pedestrian plaza, with buried traffic, is intended to smooth out the square — to remake it into a neo-Ottoman theme park. Mr. Erdogan has lately backed away from installing a mall in the faux Ottoman barracks that will go where Gezi is now. But he intends to raze a poor neighborhood nearby called Tarlabasi and build high-end condominiums. Yet another of his projects envisions a hygienic parade ground on the southern outskirts of the city, designed for mass gatherings as if to quarantine protests: the anti-Taksim. The real Taksim is an unruly commons in the middle of the city. Mr. Erdogan has already demolished a beloved cinema and old chocolate pudding shop on Istiklal (Independence) Avenue, the main street and neighborhood backbone into Taksim.