The first of the two arches that will support the Athens Olympic stadium roof is in place, organisers said on Friday.
Officials said the first 304-metre arch is now into its final position.
"Now we have the experience, the second arch will go faster. So the roof will be completed as planned," a government official said.
Fears have been raised that Greece will not be ready for the 13 August opening ceremony as several key projects have slipped behind schedule.
The huge white arch was slid along steel tracks for three days before reaching its final position late on Thursday.
The moving of the 8,500-tonne structure started on Monday, 10 days before a deadline set by the International Olympic Committeee which warned if it was not underway by then the project would be cancelled.
A second arch will also be moved into position in the coming days at the opposite side of the stadium so the latticed blue translucent roof, can cover the 55,000 seat arena.
Meanwhile, Greece's National Weather Service insists that sea breezes at the Games in August will reduce humidity to lower levels than at either the Barcelona or Atlanta Games.
"The potential of having a day with a temperature of 38
degrees or more is about four percent," they claimed.