A waxed wooden plug goes into the touch-hole.

It’s Noon on Monday, the 11th of November and half a dozen loud bangs echo across Fenny Stratford. St Martin’s church have fired their ceremonial cannon again.

The six small cannons are the Fenny Poppers. The poppers have have been fired on the 11th of November, St. Martin’s Day, since around 1740. I went to watch. At the far end of the graveyard off Manor Road, four men were preparing the poppers.

Just under an ounce of Pyrodex is poured into the cannon by Peter White.

Each one is shaped like a tankard, but they are made of gun metal with thick walls. There’s a touch-hole near the base for the fuse. Each popper is just seven inches long, but weighs 19 lbs.

Peter White of the church loaded them one at a time with just under an ounce of a gunpowder substitute, Pyrodex. It’s more stable than gunpowder, but like gunpowder it produces quite a lot of smoke when it goes off, as we will soon see.

Granborough bridge. But what's that, bottom left?

What’s this strange metal object built into the bridge? It’s an Ordnance Survey Bench Mark, and it was put there for map making. The number 1967 isn’t the year it was installed; it was built into the bridge in about 1914.

The OSBM.

There are thousands of these bench marks in the UK, numbered in sequence on long surveying lines across the country.

Visible from the Winslow road several miles away, it looks like a huge Norman castle, set against the background of the Chilterns. But instead, it’s a 1960s building right in the centre of Aylesbury.

The King’s Head in Aylesbury dates from 1455. Coaches would go through this arch when they arrived at this inn.

How do you recognise the old 18th Century turnpikes; the first decent roads to be built in Britain since the Romans left?

It’s quite easy, and there are a few ways to do it.

The first clue is the presence of milestones. If you see a milestone, you are almost certainly on a turnpike. Anciently, a turnpike was a horizontal wooden boom that turned on a vertical pivot, placed across the road until the toll keeper got your money. It came to mean the whole road.

This mile post is in Little Woolstone, in the middle of Milton Keynes.