They've been at each others' throats in 10 armed conflicts spread over 424 years; three of them across the Atlantic in South America and one that never caught fire: the "Fantastic War", so called because it involved no major battles.
Happily, Spain and Portugal haven't tried to kill each other on an industrial scale for the past 210 years. But whatever else the Iberian neighbours do in their World Cup opener in Sochi on Friday, they won't be borrowing cups of sugar.
Asked, foolishly, if Spain was Portugal's big brother, Elsa Rodrigues, a forty-something Lisboeta in mom jeans and no-nonsense hair, flashed the kind of withering eye she might level at a fishmonger trying to overcharge her for bacalhau.
"Spain is big but they are not a brother," she said, and left her words to twist in the wicked little wind that bounced off the black-and-white mosaic paving stones as it swept up the hill from the Rio Tejo.
Would Friday's game be Portugal's most difficult of the opening round? Another stupid question, it seems."If we think Spain are the most difficult to beat, it's no good," she said. "All three are very tough."
The Portuguese begrudge granting Spain a damned thing. Not even superiority.
Portugal are ranked fourth and Spain 10th. Iran and Morocco, the other teams in Group B, are 37th and 41st.
If Spain aren't Portugal's highest hurdle then there is no cult of Cristiano Ronaldo in Lisbon. And there isn't.
At least not at Benfica's official shop, where you can - for the equivalent of R14,000 - buy a replica of the inaugural European Golden Boot that Eusebio won in 1968.
About R17,000 will get you No 74 in a limited edition of 100 SJ Dupont pens, along with matching cufflinks.
Everything is Benfica branded: golf tees, Monopoly sets, jars of honey, padlocks, bottles of wine, port and ginja - the cherry liqueur Lisboetas swear offers medicinal benefits. As long as you stick to the recommended dose: seven shots for women, 14 for men. Daily.About the only floggable commodity that can't be seen in the double-storey shop is anything relating to Ronaldo. Of course not. He cut his professional teeth playing for Sporting Lisbon, Benfica's bitter rivals.
That he now plays for the most Spanish club of all, Real Madrid, only adds to the brotherly unlove.
Rui Almeida, a salesman in the shop, looks at me hard from below a tilted forehead and arched eyebrows when the player who shall not be named here is indeed named.
Almeida is a strong-shouldered young man. For a moment the smell of latent violence itself is Benfica branded. But his focus softens, or maybe it shifts to the bigger picture.
"We cannot disapprove of him," Almeida says. "He came up through Sporting but he takes Portugal to the world. That makes us feel good, so we need to be proud of him."
Ronaldo is an important part of Almeida's reasoning why "the Spanish need to look up to us, not us look up to them - they have the best league in the world but we have the best player in the world".
Almeida has yet to see Ronaldo play live. I tell him I have: in a warm-up against Mozambique at the Wanderers before the 2010 World Cup.
Ronaldo mostly went through the motions, but for a few seconds he tore upfield exponentially faster, beating opponents left, right and centre, tilting like a spinning top as he went, razzling, frazzling, dazzling, a glittering jewel on the hoof. He didn't bother taking a shot at goal, but the shock of what he could do at will is forever lodged in the memory.
Suddenly it's Almeida who's doing the interviewing: "It came from nowhere? You think, this guy, he's not human?"
Rodrigues, too, is conflicted over Ronaldo: "I'd prefer that he plays for Benfica; that's my team. But in Portugal we know he is too big for our clubs."Does she like Ronaldo as a player? She shrugs the shrug of the choiceless: "He is Portuguese, so I like him.
"Ronaldo is ..." she pauses to try to match what she's thinking in Portuguese to what she can say in English. She gives up not because she can't find the word but because it doesn't exist.
"Ronaldo is Ronaldo."..