Smoke from chimney tells the world if a new pope has been elected or not.
Work got underway in the Vatican on Friday morning to mount a chimney on the roof of the Sistine Chapel ahead of the conclave to elect a successor to Pope Francis.
The makeshift chimney stack will be used to burn the ballots after each vote by the 133 cardinal-electors after he conclave gets underway on Wednesday.
The Vatican fire brigade is expected to carry out trial runs of the chimney on Friday, according to Italian media reports.
The conclave will see the cardinals vote a maximum of four times per day - twice in the morning and twice in the afternoon - until one candidate secures a two-thirds majority.
The new pope will need the backing of at least 89 cardinals to be elected.
As part of an ancient custom, the cardinals will also use smoke from the chimney to signal to the world whether the round of voting has been decisive or not.
If the vote is inconclusive the smoke will be black. If a pope has been elected, the smoke will be white and the Vatican's bells will ring out.
Once the conclave begins, crowds gather in St Peter's Square to watch closely the colour of the smoke billowing out through the chimney, an event that occurs at around midday and 19.00.
The Sistine Chapel is currently being transformed into a venue for the secretive process to elect the 267th pope and leader of the world's 1.4 billion Catholics.
A raised timber floor is being installed along with 12 wooden tables: six on the right side and six on the left, arranged in two rows of different levels, at which the cardinals will convene.
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