Barbarian Towns don’t ever attack cities but they may attack your transports. More clearly, if you try transporting to someone of high prestige and you have barbarian cities near you, it’s believed that there’s a chance of your transport caravan getting attacked by barbarians. If they succeed, your transport caravan will be taken out, whether it be transporters or warriors and so on. They may all be killed and the resources will be taken. Often exactly half of the troops and resources will be taken. The resources don’t show up in the Barbarian Town though. You will be notified of this in a plunder report listed in black text.

yah it happened 2 me once then i went mad and took that lvl 10 npc lol
This is not true!!!!!
i got attacked now i know why