For most people, the boundary line between Gibraltar and Spain sits by the airport runway. A couple of basic buildings with passport scanners, nonchalant Spanish border guards, and occasional heady queues of traffic as the number of cars overwhelms this narrow entry into the Gibraltarean peninsula. In the morning, if I pause, I can watch a steady stream of office workers – most of them informally dressed and on their way to work in web and customer service support at the gambling companies based here. There might be a few early rising tourists. Defined by their smiles and meandering pace. For them, crossing this international border is a novelty. A few times I’ve stopped to help them take photos at the British red telephone box, the first thing you see as you step out onto the Gibraltar side. On the Spanish side: snack sellers – Moroccan men in tracksuits bottoms with fizzy drinks and novel fruit on display, cigarettes hanging out of their mouth; and the Jahovah’s witnesses – pressed clothes, sunglasses, and occasional smiles. They’re on a modernisation steak. Carrying bright pamphlets named “Anxiety” and “Why do good things happen to bad people?”. Tapping straight into the commuting malaise. Then there are the cigarette smugglers – nonchalantly meandering past. Guess who has stashed a carton of low taxed Gibraltarean cigarettes into their coat pocket or the back of their motorbike. A packet of 20 cigarettes might cost £2.50 in Gibraltar, and it’s sold for almost double that in Spain. The guessing game is worth a few hundred million pounds every year to an economy, and the illicit salary of many. It’s something that justifiably flares up tempers between Gibraltar and Spain. I’d be too skinny to play along. They fat women are best, with more folds and places to hide them.

But for me, the true frontier is a couple of blocks into Spain. I’ve stayed in an apartment building that right sits upon it. There’s poignancy to feeling yourself on the line between countries. And its not just megalomania on my side, I have history too. The garden grounds of this block are bordered by an imposing chunk of wall from the 18th century. It stretches about 50m to the east, where it’s interrupted by a road, before reaching the ruins of a fort at the beach side. Santa Barbara fort, now just a historical curiosity. A wooden walkway takes you around it, skirting the waves, and – in the summer time – a couple of beach bars.There might be surfers or fishermen as a backdrop, figurines vying for the right sea conditions.

A simple noticeboard details the story of these ruins. It was part of the linea de contravalcion, a wall which ran from here to another fort on the western side of the peninsula a little over a mile away. We know the saying a line in the sand. Well, this was the literal line two centuries ago. From behind it the Spanish placed Gibraltar under siege. For four years from 1779. It’s called the great siege in the history books. But from the Spanish perspective, it wasn’t a successful one. Britain’s maritime strength ensured that the boats could still arrive to bring supplies. And the Gibraltar rock – a military stronghold since Roman times – was burrowed to become even more impenetrable. From my old balcony view an uneven line of small holes is visible, carved out from tunnels within the upper rock. They were openings for canon fire. For the sieging Spaniards, being hit from almost a mile away was a very real possibility.

Yet enemies, then friends.The siege came to a benign end, as the two sides were united by the greater foe of Napolean at the hight of his imperialistic ambitions. Economic pragmatism took hold at the site of this wall. Spaniards settled, helping to provide the British colony supplies: meat, fruit, even space for leisure. (Things all still true today. I eat my tapas, drink my orange juice, and stretch my legs in weekend exploration on the Spanish side of life!) A frontier town was born. It was without grand ambitions, and had no history beyond this military skirmish. The wealthier town of San Roque already sat close by on a hill rise overlooking Gibraltar. This new town gained a fittingly simple name for a place of small pretension. La Linea de Concepcion. Everyone simply calls it La Linea.

The British-Spanish relationship could have created something steadily more prosperous here. Yet friends, then very uneasey neigbours. In 1969 a new Gibraltar constitution asserted it’s independence and British sovereignty. An angry General Franco ordered the closure of the border. Thousands lost their jobs. Telephone lines were severed. Relationships were split apart. The embargo lasted 13 years, and the resulting social and economic toll on the city is still visible today. Apartment blocks are paint worn, work opportunities – beyond the centre’s cluster of small shops and cafes – scarce, and I’m told that the educational system is stuttering. As both a consequence and a cause, locals turn to casual cigarette smuggling from Gibraltar. Some also turn to even more profitable drug trafficing from Morocco. I’ve watched their small motor boats rumble by at night. Men dressed in black and with holdall bars slung across their arm jump out onto Spanish sand and run-off to waiting vans or motorbikes.

Today, a stream of people drive and walk, back and forth, across the frontier. There have been recent complications. For example, in 2013 Spain ramped up boarder checks following Gibraltar’s plan to expand an artificial reef, which lead to mutli-hour queues. Though so far, I’ve been passing the boarder without a hitch. When I head into Spain, my passport barely gets a glance. Jobs, tourists, shopping, tax dodging cigarettes. They flow across day by day. The wall of the linea de contravalcion is largely gone now, just a small section remaining by the apartment block. The modern battles are instead fought over with political posturing and EU legislation. Debates that seem far away from the microcosm of life at the frontier.