The newly excavated Curtain theatre in Shoreditch is believed to be where Henry V was first performed

The battle scenes of Shakespeare’s Henry V may have been written to suit the long, narrow stage of the Curtain, one of the earliest purpose-built theatres in London.

The foundations of the theatre in Shoreditch have been excavated, revealing that it was a rectangular building with a stage about 14 metres long and five metres deep – a different shape from the “wooden Os” of Shakespeare’s more famous theatres on the South Bank, the Globe and the Rose.

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Archaeologists have discovered traces of a tunnel structure, accessed by doors on either end of the stage, which would have allowed actors to exit from one side and come on again from the other without being seen by the audience.

“The question now is whether Shakespeare and other playwrights were writing plays specifically for this kind of stage – which would have required a completely different style of interaction compared to a thrust stage with the audience on three sides,” said Heather Knight, a senior archaeologist from the Museum of London Archaeology, which excavated the site and has years more research to do on the finds.

“Did it mean that it needed a different style of acting, for instance, or that you could get more people on the stage, and so you could put in many more characters?”

Shakespeare is known to have acted at the Curtain, whose name came not from a stage curtain but from Curtain Road, which flanked a medieval monastery. The theatre was very poorly documented, but one of the few recorded facts is that the playwright was listed as an actor in the first performance of Ben Jonson’s Every Man in His Humour, in 1598.

Facebook Twitter Pinterest Battle scene from a Royal Shakespeare Company production of Henry V. Photograph: Tristram Kenton/The Guardian

It is believed to be where Henry V was first performed, and Romeo and Juliet is also thought to have been staged there. The historian Julian Bowsher believes that the famous prologue to Henry V, describing a theatre as round – “within this wooden O” – was added for later performances when the company moved across the river to the South Bank.

The theatre initially baffled the archaeologists. Its existence was marked by a metal plaque more than a century ago, but the exact site was unknown and in the only contemporary drawing of it it was shown as round.

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However, having excavated down to a layer of rubble, probably from the demolished monastery, levelled up with a layer of gravel across the entire site, Knight’s team is certain it was a purpose-built rectangular structure, with the shoulder-high stage in brick, a yard for the groundlings paying only a penny for their entertainment, and three sides of timber galleries for the better off.

It was constructed in what had been the back garden of a building on Curtain Road, and remains of green glazed pottery money boxes for the entry fees, which kept the takings safe since the cash could only extracted by smashing them, prove that it was built for paying customers.

Other finds included a comb, glass beads and pins that may have come from costumes, a clay pipe found under the stage, a broken figure of Bacchus astride a wine barrel – a fitting god for a rowdy area full of taverns – and an egg cup-sized clay vessel believed to be a bird call, possibly used for stage effects.

The design of a £750m complex of offices, shops and apartments on the site, christened the Stage, has been changed to preserve the archaeology, which will eventually be on display with the finds in a visitor centre, planned to open in 2019. The developers have also launched a poetry competition for a sonnet or a limerick linked to Shakespeare or Shoreditch, to be judged by the historian Michael Wood and Prof Stanley Wells, the chair of the Shakespeare Birthplace Trust.