A long-awaited new road and railway bridge across the River Danube is opening with great ceremony between Vidin, Bulgaria, and Calafat, Romania.
At 1,791m (5,876ft), arching 43m above the water, it is one of the longest on the Danube, and only the fourth on the lower reaches of the river.
Bulgarians hope it will revitalise the neglected north-west of their country.
Romanians fear losing precious road usage tolls from lorries on old routes close to their capital Bucharest.
The new structure adds to existing bridges at Cernavoda, between Ruse and Giurgiu, and between Vadu Oii and Harsova.
For the European Commission, which provided the lion's share of funding, the new bridge is a significant piece in the jigsaw puzzle of "transport corridors" designed to stimulate growth and opportunity across an open continent.
Ilia Iordanov, whose office is on the main road out of Vidin, has a fleet of 70 lorries, 16 Danube freight ships and four barges in his company, Fanty-G Transport.
"Crossing this bridge," he explained, "will take 500km off the route for lorries from south-east Europe and the Middle East to Western Europe."
Most importantly, he said, it will help the closer integration of rail, road, and river transport - one of the key EU objectives.
"I believe it will also encourage Macedonia and Serbia to lower their road tolls," he added.
At the moment on the old "diesel road" through the Balkans - the shortest of the options for freight from the Port of Piraeus - lorries wait for days crossing out of the EU from Greece into Macedonia, and several more days crossing back into it from Serbia to Hungary.
"So much of the cost of goods lies in the transport," Mr Iordanov said.
"I'm deeply convinced that some of the new wealth travelling past Vidin will stay here, and bring investment to the area."
He waxed lyrical about the local soil, the excellence of vegetables and fruit grown here in communist times and how the bridge would re-connect north-west Bulgaria to markets far and wide.
In the bus station in Vidin, Krassimira Senova shared his enthusiasm.
Her Eurotouring company has promised its customers that the first coach on their new Vidin to Craiova route will roll over the bridge at dawn on Saturday.
Only 84km away, many Bulgarian students go to university in Craiova but until now they faced the dilemma of either an expensive ferry crossing or a huge detour, to cross the old Friendship Bridge at Ruse, then double back.
"Students will be able to get to school in little more than an hour, instead of half a day," Ms Senova said.
She was also planning new routes to Timisoara and tourist excursions to Dracula's castle in Bran.
In a part of Bulgaria where everyone counts their stotinky - the smallest unit of the leva currency - she calculated that the bridge would enable her to cut between 50 euros (£42; $67) and 100 off the price of a week's excursion per person, whether to Transylvania, or to Paris.
In the carpentry workshop he shares with his mother and father inside the Ottoman-era fortress of Baba Vida in Vidin, Ognian Evgeniev explained that taking a lorryload of his chipboard furniture to Craiova cost 350 euros before the bridge was built.
Now it will be barely more than the diesel cost for the 180km round route.
His parents Veni and Iliana make beechwood childrens' swings, cots and toys. Veni gave up his job as a television repairman ten years ago, when he saw a niche for himself in the children's toy market in Bulgaria. Now he hopes for the same success in Romania.
Sitting at a cafe, close to the pretty Danube shoreline in Vidin, with its ice-cream stalls and fish restaurants, the head of the chamber of commerce, Krassimir Kirilov, sounded a note of caution.
"It's twenty years since many people in this region had a job," he said.
"Many young people have left the area. We are not yet in a position to offer investors a skilled workforce."
He saw the best chance in turning Vidin into a transport hub. Transformed from a backwater into a road, rail and river crossroads, it could become a centre for spare parts from all over Europe, he suggested.
On the edge of town, an old industrial estate stands gaunt and empty, offering unlimited space to would-be investors.
"I don't think we should pretend that this is the missing link of a well-structured, ready-built network," said Shirin Wheeler, spokeswoman for regional development at the European Commission.
"There isn't one motorway, for example, that links Romania and Bulgaria at the moment. But it will provide a real impetus."