Chinese experts have found such evidence in an imperial mausoleum that dates back 2,000 years.
"We discovered the remains of sea snails and clams among the animal bone fossils in a burial pit," Hu Songmei, a researcher with the Shaanxi Provincial Institute of Archaeology, was quoted as saying by Xinhua.
"Since the burial pit appears to be that of the official in charge of the emperor's diet, we conclude that seafood must have been part of the imperial menu," Hu said. The discovery was made in the Hanyang mausoleum in the ancient capital of Chang'an, modern day's Xi'an city in northwest Shaanxi province.
The monument is the joint tomb of Western Han Dynasty (202 B.C. - 8 A.D.) Emperor Jing and his empress. Of the 43 animal fossils found in the pit, archaeologists discovered more than 18 species, including three kinds of sea snails and one kind of clam.
"The ancient people believed in the afterlife. They thought the dead could possess what they had when they were alive," said Hu. Many royal tombs were designed and constructed like the imperial palace. The burial pits usually represented different departments of the imperial court, Hu said.
"The discovery of animal fossils in this particular pit may shed light on what the emperor ate every day." Ge Chengyong, chief editor of the Chinese Culture Relics Press, said: "The seafood may have been tribute offered to the emperor by imperial family relatives living on the Chinese coast. It may also have been businessmen that brought them inland to the capital city."
Xi'an is over 1,000 miles away from the Chinese coast; so how could the food have arrived in the capital without getting spoilt, experts wonder.
"During the Qin Dynasty (221-206 B.C.), people used vehicles with refrigeration," said Ge. "They may have put ice in the vehicles to preserve perishable cargo."
"The seafood may also have been dried before it was transported," Ge added. Alongside the shells, fossils of various other animals - rabbit, fox, leopard, sheep, deer, cat and dog - were also discovered.
"The cat was kept in the imperial kitchen to catch rats, and the other animals were all part of the imperial diet," Hu said.