“The loss of this critically important animal brings the species one step closer to extinction,” Peter Pritchard, an international turtle authority and author of the book “Rafetus: The Curve of Extinction,” said in an email from his home in Florida.

But for the Vietnamese, biodiversity may have been the least of Cu Rua’s attributes.

Of the four animals that many Vietnamese consider sacred, including the dragon, phoenix and unicorn, the turtle is the only one that exists in real life, said Pamela McElwee, a Vietnam expert and a professor of human ecology at Rutgers University. As a result, she added, Hanoi’s giant turtle was seen as an important link between “the here and now, the earthly world and the spiritual world.”

It was also a symbol of the capital’s endurance in the face of decades of war and upheaval.

Whenever a train rumbles into the Hanoi Railway Station, the conductor plays a patriotic song that chronicles Hanoi’s recovery after the Vietnam War and ends with an ode to one of the city’s most famous monuments: a shrine in the center of Hoan Kiem Lake built in the 1880s to honor the sacred turtle.

Nguyen Thi Van Anh, 40, a customer service agent at the Hanoi Railway Station, said she had never seen the turtle but always thought of it as an important symbol of her hometown.