Credits
Every photograph, and who took it.
Each image below was downloaded and visually checked before it was used. Captions on stock sites are written by uploaders and are frequently wrong — a search for Palmyra in Syria returned a photograph of Petra in Jordan, and a search for Krak des Chevaliers returned two châteaux in France. Neither was published.
Unsplash
Used under the Unsplash Licence and hotlinked from Unsplash's own CDN, which is what they ask publishers to do.
Photo by Mahmoud Sulaiman · Unsplash Licence
Photo by Mahmoud Sulaiman · Unsplash Licence
Photo by Obada Kabbani · Unsplash Licence
Photo by Ahmad Sofi · Unsplash Licence
Photo by Ahmad Sofi · Unsplash Licence
Photo by Fadi Alagi · Unsplash Licence
Photo by Wietse Jongsma · Unsplash Licence
Photo by Aladdin Hammami · Unsplash Licence
Photo by JOE Planas · Unsplash Licence
Photo by Fadi Alagi · Unsplash Licence
Photo by Wietse Jongsma · Unsplash Licence
Wikimedia Commons
Used where Unsplash has no free, correctly-identified photograph of the place at all — a search for Bosra returns zero results. Self-hosted, because Commons discourages hotlinking. Each is credited to its photographer with its licence.

Photo by AI-generated illustration (not a photograph of a real object) · Illustration made for this demo
Illustration, not a photograph. Drawn from the description of the Dura-Europos relief of Arsu the camel-rider (Yale University Art Gallery, YFE 1935.44, c. 100-200 CE).

Photo by AI-generated illustration (not a photograph of a real object) · Illustration made for this demo
Illustration, not a photograph. Drawn from the description of the paired Arsu and Azizos relief dated by inscription to 113 CE, National Museum of Aleppo.

Photo by Vyacheslav Argenberg · CC BY 4.0

Photo by Lubomir Mihalik · CC BY 3.0

Photo by Frank Kidner · CC BY-SA 4.0

Photo by Raki_Man · CC BY 3.0

Photo by Vyacheslav Argenberg · CC BY 4.0

Photo by Vyacheslav Argenberg · CC BY 4.0

Photo by Bernard Gagnon · CC BY-SA 3.0
Where no photograph was used
Homs city: No free photograph of the city itself could be verified. The Homs card uses Krak des Chevaliers, an hour west, which is what travellers actually go there for.
A photograph of the wrong place is worse than no photograph, so where nothing could be verified, nothing was used.