This is the Duke of Wellington's funeral carriage.

 Museum outing to Stratfield Saye House in Hampshire, one of the Duke of Wellington's homes, given to him by the nation after he finally saw off Napoleon at Waterloo.

The description reads:
"The lower part is constructed from metal of the guns captured at waterloo in 1815. Weighing 18 tons, it was completed in 18 days, a 100 men being employed working in two shifts. It was drawn by 12 black draught horses 3 a-breast."

The guide explained that the tight time scale was because Queen Victoria and Albert took over the organisation of the funeral and had fixed the date and sent out invitations before realising the cost of £32k had to be voted on by Parliament, which was not sitting.  One can only imagine what the 100 men working 12 hour shifts had to say. 

Apparently, also, the only black draught horses obtainable at short notice belonged to breweries, and each of them had their own route which they knew. There was no time for a run-through, so the horses had to be well controlled by the army otherwise the Duke would have visited a fair few pubs on the way to St Paul's.

The extra is self-explanatory.