WARRIORS in tartan wielding swords, a medieval fortress bustling with livestock, horses, dogs, goats and carts, huge trucks, cameras and action - the biggest TV series to be shot in Scotland has taken over one of its historic castles.

Outlander, a time-travelling US television romantic drama series with a £50 million budget, is shooting on location at Doune Castle, Perthshire, where lead actors Sam Heughan and Caitriona Balfe are at the centre of the most expensive TV production yet to be shot north of the Border.

Based on the bestselling novels of US author Diana Galbaldon, the show follows the adventures of a 20th century nurse, Claire Randall, played by Irish model and actress Balfe, as she travels back through time to 17th century Scotland and falls in love with a Gaelic-speaking young Scottish warrior Jamie Fraser.

Sixteen episodes of the "high end" TV drama, which is also being shot in a purpose built studio in a warehouse in Cumbernauld, will be shown in the summer on the Starz network in the US. Its co-producers, Sony Pictures Television, are in talks with numerous networks around the world, although no deal has yet been struck for it to be shown in the UK.

Around five of the 16 episodes of the lavish drama have been shot and yesterday cast and crew were at Doune Castle for a second period of shooting at the site.

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Doune Castle is playing a role itself: it is now Castle Leoch, the home of the clan MacKenzie in the books, and Historic Scotland, which runs the property, hopes its appearance on the show will lead to an increase in its 40,000 annual visits.

Other locations for Outlander, which has received financial support from Creative Scotland, have also included Culross and Loch Rannoch.

Fans of the books have already tracked down the shoot and had a peek at what is happening at the castle, which is closed to the public until March 22.

Much of the Scottish parts involve speaking Gaelic, which will be presented on the show with no subtitles - the actors have learned the language from Gaelic tutor Adhamh O Broin and non-Scottish actors have received help in Scottish accents and language from dialect coach Carol-Anne Crawford.

Sam Heughan, from the Borders, and trainer at the Royal Conservatoire of Scotland, is playing the main role of Fraser "who gets beaten up a lot".

He said of the series: "There is adventure, there's romance, there's historical stuff with the build-up to Culloden, so the stories really cover a wide area."

Mr Heughan added: "It's been fantastic, it is wonderful being on location, all the locations in Scotland have been glorious, the landscape is almost like another character in the show. Diana really loved Scotland and fell in love with it, and this will go across the world, and hopefully it will encourage people to come here - this is the first thing to be shot here on this scale, since the Game of Thrones pilot."

He added: "I think it will attract more productions, and the reason we are here is because of the [UK] tax breaks, so I hope there is more. I am surprised there is not a permanent studio in Scotland, but we have a great facility that they have created in Cumbernauld.

"I hope more productions can come here."

Heughan and Balfe have already attended a fan event in Los Angeles that attracted 2000 people, a sign of the fame of the books in the US and the passion their aficionados have for Gabaldon's work.

"It was like being a rock star... people had been queuing since 6am. I think they are obsessed with Jamie Fraser, he really is a great character," Mr Heughan said.

The adaptation of Outlander is written by Ronald Moore, best known for his work on Battlestar Galactica and Star Trek: Deep Space Nine.

It is not the first time Doune Castle has appeared on screens. It also starred in Monty Python's Holy Grail and, more recently, in Game of Thrones.