It's one of the most classic hard rock songs of all-time, but in recent years questions have come up about the true authorship of Led Zeppelin's "Stairway to Heaven." In 2014, founding Spirit bassist Mark Andes filed a lawsuit, claiming that the intro to "Stairway to Heaven" was similar to their song "Taurus," and after a couple of years of legal wrangling, the case is set to go to trial.

According to Bloomberg, the judge presiding over the lawsuit has rejected a bid to further delay the case, setting the stage for a May trial if it does not get settled or dismissed prior to then.

Andes had stated in his initial filing that it was his hope that Spirit guitarist Randy California, who wrote "Taurus" but was no longer living, would receive a writing credit on the song if they proved victorious in their case. If that were to happen, California's estate would receive a substantial sum for a track that has gone on to be one of Led Zeppelin's most recognized songs.

According to Ultimate Classic Rock, in October of 2014, a judge denied a pre-trial notion to dismiss the case based on the question of jurisdiction. Led Zeppelin had questioned whether or not a U.S. District Court in Pennsylvania, where the band did not reside, had a right to rule on the case. However, in May of 2015, there was a venue change with the case moving to a federal court in Los Angeles.

Just last month, the Wrap reported that attorney's for California's estate accused Zeppelin's legal team of wasting time by attempting to have the case thrown out on grounds that the late musician's trust wasn't valid. But the latest request for a delay actually came from the legal team for Spirit, who sought more time to gather information about the song's earnings only to be denied.

In order for Spirit to win the case, they would need to prove that not only do the two songs appear virtually identical, but that Zeppelin had access to the source material. The band did serve as Spirit's opening act in 1968, the year in which "Taurus" was released on Spirit's self-titled debut. The two bands also appeared together on several festivals in 1969.

The court has scheduled a settlement conference for next month as opposing parties attempt to resolve the dispute before the trial. But according to Bloomberg, Led Zeppelin's legal team say they plan to file a motion for a summary judgment to end the case. Listen to both songs below and judge for yourself:

Spirit, 'Taurus'

Led Zeppelin, 'Stairway to Heaven'

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