More than 250,000 gallons of concrete were poured over 14 hours for 1 World Trade Center starting on Tuesday night, giving shape to the base of a large fountain on the plaza level and boxes where trees will be planted.

 The concrete - which would be enough for six miles of city sidewalk - was brought in by 125 trucks and was the largest pour in the construction process to date. "You get a feel of what it looks like street level for the first time," said Steve Coleman, a spokesman for the Port Authority of New York and New Jersey. In total, more than 4.5 million gallons have been poured.

 "We have been spending the last year and a half building underground infrastructure," he said. "This finally gets the street level plaza being formed."

 Another significant milestone was the installation of the steel framework for the memorial in January.

 The entire process, which ended on noon on Wednesday, was recorded in a time lapse video and made public on the Internet. "You see all these guys like little ants," said Mr. Coleman.