Locals said they didn't recognize their city -- one being transformed by the steady encroachment on their civil liberties and by heavy-handed tactics by the government and police. Some locals are already calling it "the Turkish spring."
Since the Arab revolutions broke out more than two years ago, many in Tunisia and Egypt and elsewhere held up Turkey as an inspiration, a model, of how to implement a stable democracy and to thrive economically. Turkey was, to many, a paragon of a modern, Muslim nation.
But images of police firing tear gas canisters at protestors are shattering that image, outraging those in Turkey while inspiring new questions about the country's direction.
At first, these protests -- which began last week -- looked like the Occupy movement that has popped up in various cities around the world. They were about fighting the government's plan to turn a park next to the square into shopping mall and build a mosque nearby.
But after violence broke out Friday, outrage brought out Istanbulians from all ages and all sides of the political spectrum onto the streets.
On Taksim Sunday, all of Turkey was represented: the young and the old, the secular and the religious, the soccer hooligans and the blind, anarchists, communists, nationalists, Kurds, gays, feminists, and students.
They sang and danced, sending a message to Prime Minister Recep Tayyip Erdogan and his the ruling Justice and Development Party: "We will fight you."
It might have remained smallish and contained except for the extraordinary violence by police -- unconfirmed reports say two were killed and 1,000 injured. On Friday and Saturday, it quickly spiraled into a wider movement that left the government of Prime Minister Recep Tayyip Erdogan and the ruling Justice and Development Party in unusual isolation.
Several things have fueled the momentum. There was grumbling after parliament passed a law restricting the sale and consumption of alcohol late last month, and authorities also issued warnings about "immodest" public displays of affection.
While some protesters complain about the creeping Islamization of Turkey, others worry over the gentrification of Turkey's megalopolis, and yet others are concerned over the "undemocratic" practices of this prime minister, who seems to look to Russian President Vladimir Putin for inspiration on how to stay leader for life.
In reality, Prime Minister Recep Tayyip Erdogan and his backers have been pushing a peculiar mixture of Islam, capitalism, and authoritarianism for about a decade since assuming power.
Meanwhile, Erdogan is defiant, blaming the unrest on opposition parties allegedly seeking political gain. He said in a televised address: "Where they gather 100,000, I will bring together one million." But it is hard to imagine he can come out of all this politically unscathed. Even some prominent members of his party are contradicting the party line, saying that they will listen to the protesters' demands.
There may also be fallout abroad, but it's hardly news that Turkey's human rights credentials are sorely lacking: Turkey has jailed more journalists than Iran.
The unrest could also foil Erdogan's cherished project: Istanbul's bid to host the 2020 summer Olympics, which will be determined in September.
And it is likely to provide fodder for the naysayers to Turkey's bid for European Union membership, which is expected to advance to the next level of talks this month.
Recently, Turkey has been flooded with Arab money, fueling a financial bubble and high inflation. Some analysts privately say that many Gulf sheikhs are wary -- following the Arab Spring -- of investing in Western countries because if unrest breaks out, their assets could be frozen. And while the specter of instability in Turkey can do a lot of damage to Turkey's economy, these eager investors probably won't mind Erdogan clamping down on protestors.
More troubling is the damage to the credibility of one of the most vocal critics of the Syrian regime and a staunch Western ally in the search of a solution to the conflict there.
But the biggest problem for Turkey will still be at home.
Tens of thousands of people rallied in multiple cities on Sunday and police fired more tear gas at protesters. As volunteers picked up trash and debris in Taksim Square late Sunday, barricades remained and most believed it was the calm before another storm.
Even though the notion that a Turkish Spring is unfolding might be exaggerated, the government shouldn't ignore the outrage. Now that the resistance to his power grab and his vision to roll back Ataturk's secularism has been unleashed, it is likely the genie won't go back in the bottle.
As one Istanbul native protesting this weekend puts it, "Even if we lose, we have to stand up for what is right."