When the announcement that a trio of underground metal heavyweights planned to perform at the distinguished blues venue the Rainbow in mid-summer broke over the internet, it was greeted with some scepticism – but, lo and behold, all went as planned.

Thus, on a typically wet summer evening, Ottawa’s small but dedicated fraternity of headbangers gathered to see the gathered amplifiers of Zoroaster, Gates of Slumber and Serpentcult test the load-bearing abilities of the Rainbow’s stage.

Local quartet the Unavowed were the first on stage. Their punk-metal hybrid owes more to bands like Biohazard than the doom bands that influenced the visiting trio, but the audience seemed suitably impressed by the journeyman metallurgists’ adaptation of outlaw country chestnut ‘I’ll Never Get Out Of This World Alive’, as well as their own growly originals.

Most of Serpentcult were once part of Belgian cult favourites the Plague of Gentleman. The Ghent-based band broke up a while back so the various survivors recruited the lovely and talented Michelle Nocon to sing lead. Her clean vocal style stands in stark relief among the vast legion of Cookie Monster imitators (male and female) in metal, and put the band in the same territory as groups like Terra Firma and Spiritual Beggars.

Indianapolis' Gates of Slumber are three heavy set guys who look like they rode into town on Harley Davidsons, and quite possibly from there up the stairs to the Rainbow’s second storey dancefloor. You don't need bassist Jason McCash's ‘Mournful Cries’ T-shirt to tell you these guys have a heavy Wino influence (or share influences with the doom metal legend). Mainman Karl Simon’s voice even sounds a bit like Wino’s, but a more evident influence on his guitar playing is the electric blues, making for a proto metal sound combining Muddy Waters with Black Sabbath.

They did run into a typical doom metal problem: When several of your songs run past the 10-minute mark they’re more or less excluded from live performance (unless you’re Sunno)))). They gently turned down a request to sing ‘God Wills It’- "That would be our whole set!" Instead their set leaned heavily on tunes from their most recent album, ‘Conqueror’, and the soon-to-be released ‘Hymns of Blood and Thunder’.

Zoroaster finished things off by pummeling the crowd with a massive pile of Sunn and Orange amplification. There was some unfortunate technical difficulties - guitarist Will Fiore's microphone never cut through the mix like it should – but otherwise they turned in a very solid set of almost experimental doom rock. They also brought their own lighting gear which added some extra atmosphere, with a roadie off to the side of the stage working a box of switches with considerable physical vigour.

The band finally walked off the stage (or limped, in the case of drummer Dan Scanlan, who had contrived to break his foot a few weeks before) to the ringing of ears and a heavily reverbed and totally incoherent mantra from bassist Brent Anderson. The only recognizable part: “If you have anything illegal, please see us after the show.”