After an hour or so, a car appeared, and an Isis man drove Abu Ali to a reception house not far away. It was a large, one-storey building with a garden out back, and about a dozen other new arrivals were getting acclimatised.

'It was like an airport,' Abu Ali told me. 'I saw Americans, English, French, people from other countries – there was only one Syrian.'

For the next five days, he slept on a mattress and talked endlessly with the other migrants, who mostly spoke English. The Isis officials told them they were investigating their backgrounds.

There were chickens in the garden out back, and the emir insisted that only the Americans and Europeans be allowed to slaughter them. It was training for killing infidels, he said.

At the end of five days, the new recruits were told it was time to leave. Abu Ali got into a minibus with about 15 others into the Bel'as mountains, a dry, craggy range of dun-coloured peaks to the east of the city of Homs.

Training: Abu Ali spent two weeks in a mountain training camp where they underwent lessons in Sharia law

Indoctrination: He and 15 others were driven to the camp where they were fed a basic diet of cheese and bread

Harsh regime: The men would be woken up before dawn, then would perform the dawn prayer, before being taken outside for running and press-ups

Loyalty test: At the end of five days, the new recruits were driven into the Bel'as mountains, a dry, craggy range of dun-coloured peaks to the east of the city of Homs, for a training camp