RAS BAALBEK, Lebanon -- When the sun sets in this northern Lebanese Christian town near the Syrian border, Catholic businessman Rifat Nasrallah changes into his army fatigues and takes his post in one of five lookout spots on the outskirts of the city. From a reinforced bunker atop an empty house, Nasrallah uses night-vision goggles to monitor the mountain range that’s just a little more than 2.5 miles away, and is now home to terrorists from just across the border, members of both the Islamic State group and al Qaeda’s branch in Syria, Jabhat al Nusra.

“We’re in a very dangerous situation,” the imposing, chain-smoking commander of the Christian militia protecting the town said earlier on Saturday at his home in Ras Baalbek. "Suppose the army there loses a battle. What will happen to us?”

Hundreds of Ras Baalbek residents have taken up arms to defend their families, homes and businesses since Islamist militants reinforced their positions in the mountains along the Syrian border in March. They alternate between reconnaissance missions for the Lebanese army during the day and far-ranging patrols throughout the night.

“We have two options. One is to fight in front of our homes and die, and the second is to leave,” Nasrallah said. But then, he added: "The second is not an option.”

At the first sign of an intrusion, Nasrallah’s newly formed Christian militia has been instructed to contact the army post at the foot of the mountain, and then take positions around the town, alongside an unlikely ally: Hezbollah fighters. The members of the Shiite militia, which the European Union and the U.S. both consider a terrorist group, are concerned about the Sunni jihadis from Syria enough to make common cause with Christians. In fact, the Christians of Ras Baalbek and the Iran-backed militants are downright friendly to each other. In Lebanon’s complex quilt of sects and allegiances, they are pioneering a new approach: Christians and Shiites together, against the Sunni extremists.

Photo: Alessandria Masi

Ras Baalbek is just outside the Lebanese army’s front line around Arsal, the center of operations around here for the Islamic State group -- also known as ISIS or ISIL -- and Jabhat al Nusra. The town of Arsal is surrounded by badlands called the jurd, rugged mountainsides regarded by most as inhabitable. Now, the jurd area is split in half between ISIS and Nusra, and Ras Baalbek is on the ISIS side. By Nasrallah's estimate, there are roughly 4,500 fighters in that area.

The town is close enough to be within shelling range of ISIS positions. Last month a church was hit by artillery fire during a wedding. Nasrallah and several others were injured. That cemented the pact with the Shiites, as the Christian militia looked to Hezbollah for support.

“The only people who are protecting us are the resistance of Hezbollah,” Nasrallah said. "The only one standing with the army is Hezbollah. Let’s not hide it anymore.”

Hezbollah is Iran’s strongest proxy militia in the region. Across the border, its military support is one of the main reasons President Bashar Assad’s regime is still firmly in power after four years of the Syrian war. And on this side, Hezbollah has begun arming and training minorities threatened by Sunni militant groups spilling over from Syria. And unlike ISIS, Hezbollah demands no allegiance or conversion from the minorities it supports.

“They accept us as we are,” Nasrallah said. “They do not impose on us anything. When there’s an occasion, they come to our children’s birthdays. The people here accept that Hezbollah comes and helps.”

One of the minor ironies in this profoundly divided country is that the chief of the Christians of Ras Baalbek and the head of Hezbollah share the same last name. The Christian Nasrallah, a big and bearded man, even looks strikingly like the Muslim one, Hassan Nasrallah. At home, he has put above the threshold a large photo of his namesake -- flanked by a framed photo of Iran's Ayatollah Ali Khamenei, the supreme leader of a Muslim theocracy. And amid the family photos on the coffee table, there is one of former Iranian President Mahmoud Ahmadinejad.

Photo: Alessandria Masi

All this in Ras Baalbek, a uniformly Christian town of roughly 8,500, where a non-Christian would not even be permitted to purchase land. But the town is now wedged between a sprinkling of Shiite towns to the west and Sunni militants to the east, and has been forced to pick a side.

“I don’t call it an alliance, I call it a reality,” said Father Ibrahim, the town’s priest. If Sunni militants are able to reach the town, he explained, residents fear it would be a disaster not unlike what Iraqi Yazidis experienced on Mount Sinjar last year: a massacre.

“ISIS doesn’t just attack and leave. Their plan is to control the geography,” Father Ibrahim said. “ They would take the women, the money and the children.”

ISIS has recently been on a rampage against Christians. On Sunday, it released a video purporting to show the execution of 30 Ethiopian Christians the group kidnapped in Libya, with a warning that Christians all over would suffer the same fate unless they converted to Islam or agreed to obey the militants’ rules and pay a special tax, the jizya. The latest video bears similarities to a previous release, in which ISIS militants purported to behead 21 Egyptian Coptic Christians in Libya.

“Our destiny, even if people don’t want to admit it, will be the same as theirs," Rifat Nasrallah said, referring to those ISIS victims."The only difference between us and them is that we don’t have our heads in the sand.”

Father Ibrahim has made changes to his Mass since the town came under threat of the spillover from Syria. He said he now reinforces the idea that Christianity is a “final decision” and urges the young members of his church to join the fight and defend the town. He has encouraged his son to join the local Christian militia. He himself would fight, he said, if the town was under attack.

“Even though we are Christians and are supposed to be loving and forgiving,” he said, “we have to focus on not being weak and sticking to our land.”

Hezbollah has a lot at stake here, too. Ras Baalbek’s geographical position makes it strategically important for the Shiite militia. If it falls to Sunni militants, the Shiite towns surrounding it would be under direct threat.

“Ras Baalbek is at the point of the gun,” Father Ibrahim said. "If it falls, then the whole area will fall.”

Taking Ras Baalbek would facilitate the Sunni jihadists’ expansion in northern Lebanon. They would be able to easily consolidate territory all the way to the port city of Tripoli, where they have their second-strongest presence in the country.

That imminent danger makes Rifat Nasrallah angrier than he has ever been about the security situation in Lebanon, he said. Every other armed group, including Hezbollah and ISIS, is receiving aid from other countries, but the Christians are not.

"I have a message to the West,” he said. "In case one day these people are able to remove us from here, the next step is the Christians in the West.”