Digital Doom on the Highway to Destruction (G1)

Rodimus Prime inaccurately remembers the "greatest battle on Earth".

The battle known as Digital Doom on the Highway to Destruction took place prior to the construction of Autobot City on Earth.

An Autobot convoy consisting of Optimus Prime, Rodimus Prime, Cliffjumper, Cosmos, Mirage, Ratchet, Sunstreaker, Warpath, and Wheeljack set out to determine a building site for the city. They were ambushed en route by Megatron, Thundercracker, and Reflector. The outcome is unknown, but Rodimus Prime, at least, considered it the greatest battle in which the Transformers ever engaged on Earth.

Please don't ask us how Optimus and Rodimus were able to coexist, particularly before Autobot City was even built.

From Teletraan I: The Transformers Wiki, a Wikia wiki.