Linked by the River Taf and a shared history built on iron and coal, but some would say little else.
When I taught in Cardiff most had never been to Merthyr ; city folk so parochial.
Then there's the vernacular, of course : Valleys' up-down intonations against the squashed vowels of the city.
it's also true of the footie teams and my current dilemma is only accentuated by this.
Recently I've returned to watching Merthyr Town FC, the Martyrs at Penydarren Park, now the E-Ciggie Stadium.
It's a club owned and run by the supporters and the egalitarian spirit is ubiquitous.
My friend the the financial Whizz, who's largely responsible for balancing the books, can be found in the street before every game holding up a 'Car Park Full' sign.
Just imagine Vincent Tan doing that at Cardiff City! He'd be mobbed by discontented fans and there's no telling what use they'd make of the sign!
Merthyr's Candac Suite - once the preserve of chairmen like John Reddy and their guests - is a bar open to anyone. Alongside flags for the club is a large red one with '1831' on it, confusing visiting fans into thinking that the club was founded on that important day in working-class history.
Merthyr are doing extremely well; top of the Evo-Stik Southern League by 8 points and managed by local 'boy and ex-Wales international Steve Jenkins( I remember meeting his mam in the old Tescos and her talking about an injury keeping him out of the national team).
They have a perfect combo of youth and experience, from eager and pacey youngsters like Corey Jenkins and Adam Davies, to old hands like Gavin Williams and Ryan Green, who've done their time in many League teams.
Under Jenkins and assistant Stevie Williams (who played with my son in the same Penydarren team) Merthyr play football as it should be played : on the deck, with intense closing down and excellent movement off the ball at all times.
They're a joy to watch : confident, organised and very fit.
I saw them play Didcot in the FA Trophy , go 3-1 down , yet still come back to draw 3-3 with a last minute goal....they never gave up.
They destroyed a hapless Bashley 6-0 ( though it should've been 10) and outclassed Cinderford 4-0, despite the latter having a very good defensive record.
I've thoroughly enjoyed meeting up with old friends there and tasting the best curry and chips around.
It was strange v. Cinderford as Merthyr played in a 1914 commemorative
strip, while Cinderford's kit was exactly like Merthyr's usual home one.
Two old fells who arrived late were totally disorientated and started cheering for the opposition!
My friend suggested it was the 'Tan effect'.
The contrast with Cardiff City is as stark as the accents.
Cardiff : owned by one man, Vincent Tan, who still hasn't turned up to a home game this season.
Cardiff: managed by Tan's appointment Russell Slade, who has failed to bring the necessary flair, fire and anything like total football.
Cardiff City, the Bluebirds : my team for over 38 years, who seem destined to 'do a Portsmouth' and plummet down the leagues.
Cardiff : still play in red despite the fact that almost every fan sports the blue and bluebird badge and the most sound we make every game is on 19 minutes 27 seconds.......'We'll always be blue!'
It's worse than an omnishambles....it's a megashambles!
Tan will not back down on the blue, even though it's commercially counter-productive.
I talk to season ticket holders every week who say they won't return until he goes.....not glory-seekers, but die-hard fans.
Will the empty seats convince him?
My namesake, aged 26, has started a campaign not to renew season tickets for next season.
I'm in a real dilemma.
The Martyrs represent everything I want from football and I won't give up following them when I can.
Cardiff represent so much of what I loathe about the game.
Yet, as a fellow fan and once editor of the fanzine WTBF! told me - 'it's like an addiction....I couldn't stop if I wanted to.'
Now that my younger daughter is very enthusiastic, it has even renewed my allegiance.
Am I about to run away because we're playing so appallingly and the atmosphere's like a graveyard?
I am cynical because so many fans bought into the red when we were successful and have now abandoned it.
I believe the team, even club, are so much bigger than Tan and most of us will be there long after he has gone in search of other investments.
We need to blue and badge back desperately to unify the club, but I can't see him backing down.
Though I've not resolved my dilemma, I am inclined to stay and fight on ; it's more than addiction, it's a fundamental part of my past and that of family and friends.
STOP POTCHIN' !
Cardiff and Merthyr are so different :
25 miles apart yet the A470
could almost be a border.
'You'd 'ave been nothin' without our coal!'
I used to tell my Set 1 class
so full of their grades ;
with the Minister's daughter who'd sneer
and say - ' My mother...could actually
have you dismissed, sir!'
Never realised the language,
just used it naturally
like I had done in Pen-y-dre.
Year 7 boy, sensitive but pernickety,
'Stop potchin'!' I said, no uncertainty.
In a weir of tears he left the room.
Complained to his Form Tutor about me,
who luckily was from the Valleys :
'He called me podgy! It's not right, sir!'
And, lost in translation, he never
looked at me the same way again;
suspicious eyes....though he did stop potchin'.