The song originated from a riff that Phil Lynott had. Guitarist Scott Gorham told Songfacts
: "It's got the real sort of Irish-y feel in it. Brian Robertson and I, we came up with the harmony guitars in there. But the main riff came straight out of Phil. It's a song about ancient times in ancient Ireland, talking about the warring clans and all that."
"It was the first time that Brian Robertson and I did the bounce off lead guitar thing where he starts," he continued. "I start, he starts, I start... the back and forth. That's the first time we actually got that one together. It felt so good and it felt so right, so we then started to try that out on a couple of other songs. That was kind of a launching pad for that style of writing between the two guitarists."