The Ancients' secret to their expansion were the space bridges, a continuation of many successful building projects under Sentinel Zeta Prime. They were capable of moving Energon by transmitting it via the Geosynchronous Energon Bridge.
The Ancients created the Energon Harvesters to remove raw Energon from any source. According to Optimus Prime, the Ancients used the art of a given era to conceal hidden messages. For example, a fresco in Ancient Greece depicted a harvester, likely as a signpost to its location. They also were known to have foretold the events detailed within the Covenant of Primus.
After the Decepticons recovered an empty Cybertronian data cylinder, Megatron became determined to find out the contents of the device. This is because he believed that the knowledge of the Ancients was power. When the knowledge of this data cylinder threatened to consume Bulkhead's mind, Ratchet initially struggled with finding a means of removing the data without the wisdom of the Ancients.
During a planetary alignment, the events detailed within the Covenant of Primus of a time of darkness was coming to pass. Ratchet claimed that he always related such a story to the war that had engulfed Cybertron. However, events came to pass that this chaotic period might have related to the planet Earth instead. Megatron attempted to make the events of the tale come to pass by building a space bridge in order to harvest Dark Energon. During a battle with Optimus Prime, he told his old foe that the Ancients had foreseen his defeat though Optimus told him not to believe everything he had heard. At the climax of the fight, it was finally revealed that Earth was indeed the site of the prophecy as a large deposit of Dark Energon was erupting from beneath the Earth and coming to the surface from a volcano.