Here's why:
* Chronological Order: The Lost Books series is a prequel to the Circle Trilogy.
* Story Connections: The Lost Books series introduces characters and concepts that play a significant role in the Circle Trilogy.
* Publication Order: The Lost Books series was published before the Circle Trilogy.
It's best to read the Lost Books series first to get a better understanding of the history and background leading up to the events in the Circle Trilogy.