User blog comment:FairyRaven/Fairy Tail Chapter 336: In Order to Live Today to the Fullest, Review and Commentary/@comment-77.195.192.240-20130624072334/@comment-77.195.192.240-20130624085856

Mashima use the time travel as Stargate-SG1 use the space travel. Imagine Eclipse as the bridge of stargate between the pegasus and milky way galaxies, it's the same thing. Future Rogue and Future Lucy enter a date, a vortex is created between the starting point and the end point, but if the Eclipse gate near the date of arrival is missing there will be a problem and the vortex will be disrupt.

So a gate is also present 400 years ago, and this is this gate that the dragons used.

The timelines are there to explain things to readers, but when you read a Fairy tail chapter, you must act as a ghost among the characters