These clocks are the cathedral's voice, those that ring every day, says Philippe Jost, head of the organization responsible for Notre Dame's reconstruction.
In July, they were forced to remove the clocks from the north tower to complete the reconstruction of the cathedral.
The clocks have been cleaned from lead dust that fell from the church's burning roof and restored at a foundry in Normandy, northern France. Now they have been transported back to Paris by truck.
On Thursday, the sound of the bells will be blessed, each bell named after a significant figure in the cathedral's history.
The heaviest "Gabriel" weighs over 4.1 tons, while the lightest "Jean-Marie" weighs only about 780 kilograms.
"Gabriel" is not, however, the heaviest of all Notre Dame's 20 bells. The heaviest weighs 13 tons and hangs in the south tower, ringing at major church events such as Easter, Christmas, or a pope's death.
Notre Dame is planned to reopen on December 7.
