Editor's note: In Thursday's programme Melvyn Bragg and his guests discussed the An Lushan Rebellion, a major uprising against the imperial rule of the Chinese Tang Dynasty. As always the programme is available to listen to online or to download and keep - PM.
So Chang'an was the biggest city in the world in the 8th century and, by the sound of it, the most extraordinary. Frances Wood's description of the varieties of spectacle and people and entertainments on offer was in itself spectacular.
I think we should have defined the role of the concubine a little more closely and explained why everyone who was important in that story seems to have been excessively fat. Presumably by necessity. There was a sumo feeling about it for me.
But how wonderfully they rolled it through, the three of them. For a while I was out there in the ocean that was China, with the borders breaking up and Tibetans coming in, and incursions of mercenaries from near Samarkand, and warring warlords and separate courts...
Back into the London air and a walk to my office in Soho. London is back to its summer with a mild, chill climate. Worked there, a meeting, down to the Lords, off to another meeting; and then in Whitehall a wonderful spectacle which might begin to make London, if not the biggest city in the world (as Chang'an was) but, as some people think, the greatest, the most magnetic city in the world.
Down Whitehall came a long line of Congolese protestors. They were heading for the railings opposite Downing Street and they were escorted by policemen walking at that slow pace that we thought they used to walk at only in the past. They still can walk at that slow pace.
And on the way down they were singing these songs; women with pushchairs, men in dark glasses, children, ageing adults chanting for freedom and democracy in the Congo. It was wonderful music and just an inspiring sight, frankly. The police walked calmly and on the outside of the procession, ie. the road side, there was a white tape which, fragile though it was, kept the protestors in a very manageable line.
But, for me, the best thing of all was that when you came to the end of the line, there was a man following the procession, carefully winding up the white tape so that everything would be neat and tidy when the congress eventually reached the railings opposite 10 Downing Street. There was a line of yellow-tunicked policemen in front of 10 Downing Street and behind them the great gates.
I can't be the only one who has a little pang of pride that once upon a time Downing Street was just another street, and you could walk in and look at the door used by the Prime Minister of not only a country, but countries and even an empire.
It seemed to be such a proud and magnificent contrast - the "humble street" from which so many red patches on the globe were run.
There was even, within living memory, tales of a Prime Minister who hadn't particularly liked the house and used to go home to Hampstead on the bus. On the bus! Nowadays, he would go home to Hampstead surrounded by armoured tanks.
I wonder what would happen if we dropped all security for a few days and had a go without it? Might freshen things up.