Greenwich Meridian

It's an imaginary line. Last night, as my bus returned from Barcelona to Zaragoza, at about 4am, we passed a point on the road where this imaginary line is celebrated with signs that say - Meridiano Greenwich - 3kms and then Meridiano Greenwich 1500 mts and then, there it is, an arc of light crosses above both sides of the road. Is it a bridge, or just an arc? I don't know, couldn't tell. But I thought it was curious that this imaginary point that crosses from London to Spain to other countries and separates the Western Hemisphere from the Eastern Hemisphere (totally imaginary and I suspect, a bit arbitrary)had a physical touristy representation in the middle of a road in the Aragon Region. Wonder who decided to spend tax dollars on that. Anyway, here's a link to a wikipedia article about the Greenwich Meridian and what it's used for if you're curious
http://en.wikipedia.org/wiki/Greenwich_meridian