Fourteen times the earth has made its great march through the heavens since the work began. The vicissitudes of fourteen years have tried the courage and the faith of engineers and of people. At last we all rejoice in the signal triumph. The beautiful and stately structure fulfills the fondest hope. It will be a source of pleasure to-day to every citizen that no other name is associated with the end than that which has directed the work from the beginning—the name of Roebling. With all my heart I give to him who bears it now the city's acknowledgment and thanks. What is the central idea of this excerpt?