TURKEY-SYRIA BORDER -- Turkey's frontier with Syria is mountainous and 500 miles long. The entry point for thousands of foreign fighters who have come here to join ISIS.
For decades, Turkey's border with Syria has been notorious for smuggling - but now, along with contraband - the smugglers spirit people into the war zone.
In one village, we met a man who refused to show his face, but he told us he made a living getting people in and out of Syria illegally.
He told us he helped around 20 or 25 foreign fighters from Chechnya and Indonesia, and one who came from London, get across the border.
Europe's counterterrorism chief says 1,000 Europeans have joined ISIS and other militant groups in the last three months alone.
Three young British Muslims even starred in an ISIS recruitment video.
"Look around you where you sit in comfort and ask yourself is this how you want to die," they ask in the footage.
Others have come here from places like Saudi Arabia, Libya, Yemen - and the U.S.
The latest ISIS propaganda video features a man with a distinct North American accent. "The flames of war are only beginning to intensify, the fighting has just begun."
Turkey says it's beefed up security on its border with Syria, posting more soldiers, and building a new wall to stop smugglers. But it only extends for a mile and it won't be enough to stop young Muslim men who are determined to join the cause of Islamic extremists.