The formidable defenses were built on bitter experience.
In the 17th century B.C., a people known as the Hyksos invaded from Canaan, sweeping across the Sinai to rule over the Nile Delta and northern Egypt.
The Hyksos' reign faded about a hundred years later. Subsequent pharaohs cast a wary eye to the east and militarized the northern Sinai.
By the reign of Ramses II, who ruled from 1279 to 1213 B.C., a new enemy was on the horizon: the Hittites, who came from present-day Turkey and battled the Egyptians until around 1258 B.C.
"The fort, built to secure the entrance to the Delta and protect Ramses II's city of Piramesse, demonstrates the importance to the Egyptians of securing the eastern border," Hawass said.
"The need to protect Egypt's eastern frontier was made clear by the invasion of the Hyksos, who were able to cross the desert into Egypt and establish themselves as rulers in the Delta region."
Much of this maneuvering is described at Karnak, the massive temple complex near Luxor.
(Download a wallpaper photo of the temple at Karnak.)
"The most surprising thing about the fort is how accurately its architecture was depicted [at Karnak]," said Hawass, who is also a National Geographic Explorer-in-Residence.
"The archaeologists have found evidence of the exact buildings shown, as well as of the moat which surrounded the citadel and of the large, wooden beams which spanned it."
An expedition led by archaeologist James Hoffmeier of Trinity International University in Deerfield, Illinois, unearthed a smaller fort known as the Lion's Lair about four miles (seven kilometers) east of Tjaru at Tell el-Borg.
(Read related story" "Ancient Egypt Cities Leveled by Massive Volcano, Lava Find Suggests" [April 2, 2007].)
Another small fortress 7 miles (15 kilometers) away was unearthed by a French team.
Free Email News Updates
Sign up for our Inside National Geographic newsletter. Every two weeks we'll send you our top stories and pictures (see sample).
SOURCES AND RELATED WEB SITES