It was a strange, weird barrier, this vast hedge of cactus and thorny acacia, of prickly palms and agaves that thrust out their spiked swords boldly from a buckler of spine-set thicket.

Welcome to the documentary in the studio from the BBC World Service.

This is the series that gets inside the minds of some of the world's most creative people.

I'm Paul Waters and I'm following the Indian artist Himali Singh Soin

and her creative partner and husband, the German artist David Soin Tapasur,

as they create new exhibitions in two of Britain's most prestigious galleries,

inspired by an almost forgotten part of India's colonial history around the taxation of salt.

That opening quote, read by Himali, is from Flora Annie Steele's autobiography, The Garden of Fidelity.

She was a prolific British author who lived in India, and her writing is an important reminder of a now vanished barrier that once stretched for 2,500 miles across India.

What a barrier it was, 40 feet high by as much broad, over which birds, butterflies and dragonflies fluttered, while on the

round fleshy leaves the coccanial insects gathered, like tiny spots of blood, scarlet.

I'm at Somerset House in London, a former Royal Palace and later on headquarters of the Royal Navy.

It also used to house the salt taxation offices, which is very relevant to Himali and David's salt theme.

Their exhibition here has three parts.

The first part is a very large scale reimagining of the inland customs barrier or salt line,

which divided India for most of the 1800s.

It was created by British colonialists to restrict the movement of salt so they could tax it.

Work on setting up the artistic representation of it here has just begun,

and this is the first day that David and Tamali are seeing how their idea is becoming reality.

Their salt barrier is currently only a thin line of white steel bars,

twisting and turning along the cobbles of the courtyard.

What we are looking at at the moment is an imagination of the map of the Indian subcontinent

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