Until the 2010s, Amapá, Roraima and large parts of Pará and Amazonas sat outside the Brazilian grid. They ran on thermal generation: diesel and gas, expensive, dirty and subsidised by everyone else. Manaus had the Balbina Dam nearby, a notoriously poor bargain that drowned a great deal of forest and still supplies under a fifth of the city's power. The Tucuruí dam, meanwhile, sat south of the Amazon with 8,370 megawatts installed - the country's third largest hydroelectric plant, after Itaipu and Belo Monte - and no way to send a watt of it north. The Tucuruí-Macapá-Manaus interconnection was the answer: a 500 kV double circuit from the dam through Anapu, Almeirim, Oriximiná and Silves to Manaus, with a 230 kV branch peeling east from Jurupari through Laranjal do Jari to Macapá. Total transfer capacity, 2,400 megawatts.

Building it meant crossing terrain that does not accommodate heavy machinery. The route was kept alongside existing highways wherever possible, and where the line had to cross standing forest, engineers raised unusually tall towers so the conductors could clear the canopy rather than cut a gap through it. Between the Xingu and the Amazon lies the Alagados: seventy kilometres flooded in the rainy season and deep mud in the so-called dry one. Large barges were out of the question. So the contractors built light ones and propelled them with a hydraulic excavator mounted at the bow, the machine reaching forward and hauling the whole vessel along by its own bucket, one scoop at a time. To find the deepest channels, crews followed the trails made by water buffalo. Four thousand workers lived in fourteen camps.

The river crossings - the Amazon, the Trombetas, the Uatumã - demanded a different order of structure. At Jurupari the line makes a 1.2-kilometre jump between 150-metre towers, then the big one: 2.2 kilometres between the 295-metre giants, the strain section running 3,908 metres end to end. Chinese contractors built the two towers and the main span - Zhejiang Electric Power Transmission and Transformation Corporation, with the China Cable Corporation and Zhejiang Shengda - using stranded aluminium conductors over steel cores. Alongside the power cables the project strung optical fibre, installed by TIM Brasil in just seventeen spans - made as long as possible, because nobody wants to maintain a signal-regeneration hut in the middle of the Amazon. The line carries broadband as well as current.

Power reached Manaus in 2013, two years past target, at a total investment of US$2.29 billion. The northern extension, 750 kilometres on to Boa Vista, ran into something no engineering could solve. The chosen route follows the BR-174 highway, and 123 kilometres of it, carrying about 250 towers, cross the Waimiri Atroari Indigenous Territory. The only route that avoided the territory ran 902 kilometres and would have opened roads into better-preserved forest - a real argument, but not a substitute for consent. The Waimiri Atroari had already lived through the driving of BR-174 across their land, through what is remembered as a violent “pacification”, through illegal mining, and through the flooding of sacred places behind the Balbina Dam. When public hearings were held, they took place in Presidente Figueiredo, Manaus, Rorainópolis and Boa Vista - not inside the territory. In February 2016 a federal judge halted work on the 500 kV line, finding that the free, prior and informed consultation required by the international convention on indigenous and tribal peoples had not happened. A month later another judge suspended that injunction, ruling that the licensing of a project of national strategic importance had been improperly interfered with. Boa Vista, a city of more than 400,000, went on losing power meanwhile, on an ageing line from Venezuela.

A transmission line in the Amazon is not only its towers. Beneath the conductors runs a maintenance corridor up to seventy metres wide, and for a great many forest animals seventy metres of open ground is a wall. In 2014 scientists at the National Institute for Amazonian Research warned that the Boa Vista section would cut past the Adolfo Ducke Forest Reserve - one of the most intensively studied patches of rainforest anywhere - and risk isolating it. A prosecutor opened an inquiry in 2013 over trees felled in Manaus's Mindu Park in apparent breach of the licence; in April 2015 R$450,000 went to the Uatumã Sustainable Development Reserve as compensation for impacts described as irreversible. Set against that is the accounting the project was sold on: replacing subsidised diesel and gas with hydroelectricity is estimated to avoid about 1.46 million tonnes of carbon dioxide equivalent a year. Both things are true at once, which is what makes Amazonian infrastructure so hard to argue about honestly.