Hello and welcome to the Intelligence from the Economist.

Today from London, I'm your host Jason Palmer.

Every weekday we provide a fresh perspective on the events shaping your world.

In Zimbabwe there's a colossal wall of exquisite dry stonework in circling what was once

a community of 10,000 people.

The site's secrets are slowly being uncovered, but the fact that so little is known reveals

much about archaeology's biases.

And our final story has about a one in five chance of being a stimulating sensory experience

for you.

We explore an exhibition dedicated to ASMR, the thrill that some people get from simple

sounds such as the folding of shirts or wrapping of presents.

First up though.

Britain's Prime Minister Boris Johnson made a momentous trip this week to Sweden and Finland.

He struck a collective defence agreement with both countries leaders.

From the high north to the Baltics and beyond our armed forces will train, operate and

exercise together.

In substance it's a lot like Article 5 of the NATO Treaty.

Any of the countries will come to the others aid if attacked.

Yesterday Finland's president Sally Nini Sto and Prime Minister Santa Marin announced their

backing for a bid to join NATO after decades of being formally nonaligned.

For us, turning NATO would be not against anybody. We would like to maximise our security,

but it is not a zero-sum game.

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