Special Autobot prison
From Transformers Wiki
A mighty foe requires a special prison, and that's why Megatron has had a special Autobot prison built to hold them in. Unfortunately he built it before he and his men had any idea how they were going to get the Autobots inside it, but those details can be worked out later.
Fiction
Coloring books
Once the prison was completed, Megatron instructed his men to trap the Autobots so they could be imprisoned within it. With the aid of Sleep Nets, the majority of the Autobots were soon rounded up and the Decepticons could carry on with their plans to conquer Earth without danger of being foiled. Unfortunately they'd overlooked Bumblebee. While Spike and Sparkplug Witwicky kept the Decepticons distracted, Bumblebee slipped into the prison and freed the other Autobots. Bumblebee to the Rescue!