Teaming for their first co-production, Amazon in the U.S. has joined with the UK’s Sky on original drama series, Britannia. Written by Jez Butterworth, this will be Amazon’s first series entirely produced overseas. In April, Deadline revealed that Kelly Reilly was in talks to star; she will now be joined by The Walking Dead‘s David Morrissey along with Zoë Wanamaker (Harry Potter And The Sorcerer’s Stone) and Stanley Weber (Outlander).

Vertigo Films (Monsters) is producing the 10-part event drama in association with Penny Dreadful‘s Neal Street Productions.

The story is set in 43 A.D. and charts the Roman invasion of what would become Great Britain. The determined, yet terrified, Roman Imperial Army returns to crush the Celtic heart of Britannia, a mysterious land ruled by wild warrior women and powerful druids who can channel the forces of the underworld.

Reilly and Wanamaker play arch-rivals Kerra and Antedia who must set aside their differences to combat the invasion, led by the towering figure of Aulus Plautius (Morrissey). Hugo Speer, Nikolaj Lie Kaas, Stanley Weber, Eleanor Worthington-Cox and Ian McDiarmid round out the cast.

Shooting on location in Prague and Wales, Britannia will air on Sky 1 in the UK and Ireland and be available on Amazon Prime Video Stateside in 2017.

Vertigo’s James Richardson will executive produce with Pippa Harris and Nicolas Brown from Neal Street, and Anne Thomopoulos (Rome, Band Of Brothers). Star Wars’ Rick McCallum produces. Jez and Tom Butterworth (Fortitude) are lead writers with Richard McBrien (Spooks). International sales will go through Sky Vision. WME and Sky Vision negotiated the deal with Amazon.

Butterworth, whose feature credits include Spectre, Black Mass and Edge Of Tomorrow, calls the drama “the Heavyweight Clash of All Time, the one which most shapes who we are today. And we see it all from a human perspective, of individual survival, ambition, courage, lust, loss, revenge.”

For Sky, Britannia joins such upcoming originals as The Young Pope, whose first two episodes will premiere at the Venice Film Festival; Guerrilla; Tin Star; Delicious; Riviera; Jamestown; and The Last Dragonslayer. Amazon’s originals on deck include Goliath, Good Girls Revolt, Sneaky Pete and Patriot.