I notice that many people have said that the gauge at the colliery where George Stephenson worked was 4 ft 8½ in. It wasn't. According to Andrew Dow (The Railway, British Track since 1804, Pen and Sword, 2014, p.110) the gauge at Killingworth Colliery was 4 ft 8 in. The extra half-inch "crept in" between Stephenson's time at Killingworth and the Rainhill Trials in 1829. It is likely that engineers found that they needed the extra half-inch gauge widening on curves, so they added it everywhere.

Sorry to appear pedantic, but it's best to get the facts right, or they will be promulgated wrongly for ever.

No need to apologise!
Quite right that we need to get the facts correct, like the myth about the Great Central's London Extension being built to 'continental loading gauge' which just isn't true, but people believe it as it's in a couple of books....

Going back to the conversation about early engines and tall funnels - Eric Steward was stationmaster at Lime Street, and once took me and the boys from my school model railway club onto the sidings at Edge Hill - the site of the early station.  On one side of the deep cutting the remains of a wooden staircase zig-zagged down the rock face, and on the other were the caves in which the locos were "stabled" overnight.  They were turned ninety degrees on turntables in the track and pushed in.  Every cave had a rounded roof with a large groove in the centre to accommodate the folded-down funnel.  The track was not a through track anymore, but Eric had used some European grant money to put a relief siding down the cutting in order to preserve a piece of history.  GoogleEarth  53°24'5.57"N  2°57'1.04"W  He had also had the entrance path to the station "paved" with the quarters of the early wooden wagon wheels. A true railwayman! 

That's Crown Street isn't it?

The siding now ends in Crown Street Park, Overbury Street. 

Yes it does.

Idling an hour in the departure lounge at Austin airport, I rediscovered yet again that 1435mm of track gauge fame is the circumference of a 9 inch circle. Now to find a fanciful explanation for that coincidence that does not involve a horse's haunches, or George Stephenson.

To show how my idling mind works, at the recent Bachmann open day in the Dean Forest, I drove Class 08 D3937.   39.37 inches= 1 metre.

It actually would make sense for some wagonways and later railways to have used "a" standard that already existed. From what I have read, some Roman streets were designed as both roadway and drain/sewer, with raised pavements forming the sides of the channel. To cross from one side to the other, stepping-stones were provided ... which of course would have had to have had a standard spacing, to be matched by chariots, carts or whatever, so that wheeled traffic could pass between the stones. If the Romans built such streets here, that would have set the same spacing. Even after such streets disappeared, the dimensions might well still be used, due to it being standard, existing ruts, wheelways on bridges, etc. and that would, in turn, have lead to wagonways matching existing carts. There's nothing to say that that happened, but it would be feasible.

Not all of the early railways in Britain were built to what we now call standard gauge. At least one very early Cornish horse drawn railway was built to 4 foot gauge. However, if you visit Pompeii and check out the ruts in the cobbled streets which were made by Roman vehicles you will find the gap between these ruts is very much around "standard gauge".

The Scotch gauge as it was known as, was 4ft 6 inches, the Irish Gauge was / is 5ft 3 inches.

For a period that ended in 1996 (from late 60s?) the BR gauge was not 1435mm (4ft 8 1/2in) but 1432mm (4ft 8 3/8in). This was an idea to reduce hunting by worn wheels... in 1996 they realised eventually they'd have to cut the gauge again as the wear just appeared in a different place.. So it was dropped as a silly idea..

So you know how to really annoy a P4 /S4 modeller of the  1980s period... tell him his track gauge is wrong..

The Roman 'War Chariot' is a myth. While a ceremonial Quadriga (4 horse chariot) was used in a formal 'Triumph', (Celebrating, at least initially, a exceptionally successful general.) Romans regarded the Chariot as old fashioned and unable to compete with cavalry and no threat whatsoever to their Heavy Infantry.