Start the Week is at the Radio 3 Free Thinking Festival in Gateshead. Anne McElvoy talks to the historian Catherine Merridale about the Kremlin - a Russian fortress which has retained its original medieval function to intimidate and control, and which holds a special place in the imagination. Few buildings in England inspire such fear, but Simon Thurley explores how the country's architecture has influenced the world. The Newcastle-born writer Michael Chaplin looks to the history of the River Tyne to understand the changing fortunes of the city and its population; and the Indian writer Amit Chaudhuri attempts to save the remnants of Calcutta's colonial past under its ever-changing skyline.