Two tunnelling machines bought to help build HS2 have been unveiled by the firm behind the high-speed rail line.
The excavators will bore a 10 mile (16km) tunnel through part of the Chilterns, from a site near the M25 to near South Heath in Buckinghamshire,
HS2 Ltd chief executive Mark Thurston said the machines would "be a defining moment in the history of HS2".
The two 2,000-tonne machines, built at a factory in Germany, will dig as deep as 80m (262ft) below ground.
They have been named Cecilia and Florence, after Buckinghamshire-born astronomer Cecilia Payne-Gaposchkin and Florence Nightingale, following a public vote from a shortlist of suggestions made by local schoolchildren.
The plans for HS2 were first outlined more than a decade ago. The initial stage, due to be completed between 2028-31, will connect London and the West Midlands, while the second section will extend into the East Midlands and north of England.
HS2 minister Andrew Stephenson said: "HS2 will provide better, more reliable connections that truly level up our country, boosting economic growth and sharing opportunities."
Florence will be launched in early 2021, with Cecilia beginning the other half of the tunnel about a month later.
Both machines are 170m (558ft) long and have been designed for the chalk and flint under the Chilterns.
They will run almost non-stop and are expected to take about three years to excavate the tunnel, which will be lined with concrete.
Source: BBC