A Hundred Years Ago was a poem written by Rodrick Heffley for history class while he was in middle school. When Greg received the same assignment years later, Rodrick sold him this poem for $20,000 Mom Bucks (or $200 in real money). Greg soon realized that this was not a good idea, as the poem was quite poorly written and Rodrick later discovered that Greg had stolen the Mom Bucks from Rowley's Monopoly game rather than actually earning them.
- This poem is quite inaccurate, as Rodrick only describes things that might have happened at the beginning of the Earth (rather than actual events that happened in the previous century), and nonsensical things such as giant spiders ruling the Earth. It would have made more sense if Rodrick had called this poem "A Hundred Million Years Ago."
- The poem from the movie is slightly different than the one from the book.