Authorities searched the vehicle in Siegen, North Rhine-Westphalia, on Friday, with drug dogs leading officers to wooden crates stuffed with bales of cannabis.
The raid was the culmination of an investigation into a suspected drug dealing ring.
“It is a sensational and absolutely formidable blow to the organized drugs scene,” Siegen narcotics officers said in a statement.
The investigation initially took officers to a warehouse in Ferndorf, near Siegen. They then searched a truck where they made the discovery.
The haul took up 22 cubic metres of space inside the truck and is worth several million euros. It was divided into 10-kilo bundles.
Police arrested five people, all of whom were on still in custody on Monday.
They are, police said, aged between 29 and 56. Two were drivers from Italy. Two others are Albanian and the last a German-Albanian.