Residents chafe at the radical changes, and some are starting to rebel against the militants as they try to "cleanse" the region of anything — and anyone — deemed non-Islamic. As many Christians in Mosul have discovered, their only choice is fleeing.
"I was shocked when I heard the new decision forcing me to wear a veil and totally cover my face," said Mais Mohamad, 25, a pharmacist in Mosul, the second-largest city in Iraq. "I can't do that — I was always free to wear what I like. I can't live the rest of my life with my face covered."
The militants, an al-Qaida splinter group so radical that it was rejected even by al-Qaida, initially concentrated on providing services such as sanitation and restoring order. The group, which insists on being called the Islamic State, issued religious decrees soon after taking over the city but didn't enforce them, residents said.
During the past few weeks, the group has begun to crack down in an effort to fulfill its ambition to create an Islamic territory spanning Iraq and neighboring Syria.
"The Islamic State of Iraq and the Levant [the group's original name] decided that anybody who utters their [old] name will get 70 lashes," said Ghaida'a Al-Rasool, a doctor in Mosul. "Their new name is simply the Islamic State."
The group has established Islamic courts controlled by muftis, or Muslim religious leaders. Fighters regularly drive through the streets in trucks using loudspeakers to inform residents about changes.
"They have told clothing merchants to sell what they have within 20 days and then only jubbas are allowed," said Saad Al-Hayali, an engineer in Mosul, referring to flowing, one-piece robes worn by Muslims throughout the Middle East. "They have forbidden dressing rooms inside stores, too."
More worrisome for residents is the Islamic State's move to cleanse its strongholds. Christians and other minorities were given an ultimatum: Convert to Islam or face execution.
"I left from my home when we received the threat," said Abir Gerges, 45, a Christian schoolteacher who fled to Irbil, a city in Kurdistan, a semiautonomous region of Iraq protected by its own military force.
"I told my husband, 'We have to leave,' " said Gerges, a mother of three boys. "He hesitated, saying, 'How can I leave the house I inherited from my parents?' But I told him they might kill us and kill our sons in front of us. What are we going to do with a house if that happens? So he decided to listen to me, and we took our money and my jewelry and a bag of clothes and left."
Gerges and her family quickly saw the scope of the militants' rule when they came upon a checkpoint far outside Mosul.
"I put on a veil, trying to hide, but they asked if we were Christian," she said. "We were afraid to lie to them, so we said yes. One of them — he was masked — advanced toward me and said, 'You must remove all the jewelry you are wearing. Now it's Islamic State property.' Also they confiscated all my husband's money. Afterward, they said, 'Now you can go. That's punishment for your refusal to be Muslim.' "
The new rulers are wiping out traces of churches and ancient shrines.
"The churches are closed," said Al-Rasool, the Mosul doctor. "Yesterday, I saw an old church in the streets of the Ras al-Kur historic district. The doors of the church were walled off with cement and blocks."
City Hall employees are expected to continue coming to work, but tolerance for non-Sunni Muslims is slight.