Professor Mary Beard broaches the controversial, sometimes dangerous, topic of religion and art. For millennia, art has inspired religion as much as religion has inspired art. Yet there are fundamental problems, which all religions share, in making the divine visible in the human world. How, and at what cost, do you make the unseen seen? Beneath all works of religious art there always lies conflict and risk. The result is often iconoclasm - the destruction of works of art - which Mary believes can lead on to new forms of creativity.

Mary visits sacred sites across the world to examine the contested boundaries between religion and art. She goes to the temple of Angkor Wat, the Tintoretto Crucifixion in Venice, the Buddhist caves of Ajanta and the Blue Mosque in Istanbul, as she seeks to break down the conventions that centre some religions around images, while others are seen as hostile to artistic representation. She shows how all faiths (and their artists) face the same fundamental problems of treading a careful line between glorifying gods in images and blaspheming by daring to represent the divine.

She ends at the Parthenon in Athens, a building that has been in turn a pagan temple, a Christian church and a mosque. Now, as a monument to Western civilization itself and a tourist pilgrimage site, she asks us to wonder what we now worship - how far we look at civilization itself with 'the eye of faith'.

In the 15th and 16th centuries distant and disparate cultures met, often for the first time. These encounters provoked wonder, awe, bafflement and fear. And, as historian of empire David Olusoga shows, art was always on the frontline. Each cultural contact at this time left a mark on both sides: the magnificent Benin bronzes record the meeting of an ancient West African kingdom and Portuguese voyagers in a spirit of mutual respect and exchange. By contrast we think Spain's conquest of Central America in the 16th century as decimating the Aztecs and eviscerating their culture.

But David shows even in Mexico rare surviving Aztec artworks recall a more nuanced story. He travels to Japan to explore how the Tokugawa Shogunate, after an initial embrace, became so wary of outside interference that they sought to cut ties with the outside world. But in their art, as in their trade, they could never truly isolate themselves from foreign influences. By contrast the Protestant Dutch Republic was itself an entirely new kind of creature: a market driven nation-state. It was a system that created new freedoms and opportunities as embodied in the world-infused art of Johannes Vermeer, or the watercolours of the naturalist and illustrator Maria Sibylla Merian.

David ends with the transitional story of the British in India: at first the British were as open to foreign influence as the Dutch. But by the 1800s they became more aggressive and the era of encounters gave way to the era of muscular empire, that was dismissive of India's arts and cultures.