Every week, on Saturday at 18.00 (+3 GMT), a tribute wagon leaves from Balenos-1 Velia and travels to Calpheon. The wagon carries the earnings of the siege guild that won Calpheon that week and is full of silver. As you attack the wagon, it drops silver. You can make up to 300 million in 20 minutes if you have enough AP. PK opens up automatically around the wagon (you will not lose karma) and in order to avoid damage from the other players, we build a platoon including every person who joins the wagon heist.
However, the siege guild can come to defend the wagon. When this happens, the protectors of the wagon become immortal. It is not possible to hurt or kill them around the wagon. In order to protect our members, we bring our guild elephants to the wagon heist. If you cannot protect yourself, you can ride the elephants and attack from there.
You can learn more about wagon heists from here.