Saint Hilarion, which is located at a site called Tel Umm al-Amr, draws its name from the fourth century hermit who came from southern Gaza and is considered to be the father of Palestinian monasticism.
Its life close to the Mediterranean shore spanned more than four centuries -- from the late Roman Empire to the Umayyad period. Abandoned after an earthquake in the seventh century, it was uncovered by local archaeologists in 1999.
But today, "it's a complete mess -- archaeologically, scientifically and on a human level," laments Rene Elter, a researcher at the Ecole Biblique, a French academic institution in Jerusalem, who is responsible for trying preserve the site.
"We have to save Saint Hilarion," Elter told AFP. "The situation is critical and we risk losing the site. It is imperative that something is done quickly; otherwise it will be lost, lost forever."
Just over a year ago, the Palestinians submitted Saint Hilarion to be included on the World Heritage List of UNESCO, the UN cultural organisation.
The World Monuments Fund, a New York-based group dedicated to preserving the world's architectural heritage, last year put it on its Watch list. This is includes sites around the globe at risk from the forces of nature as well as social, political, and economic change.
But there isn't enough money to do the job.
Elter believes the cost of saving the site, located near the Nusseirat refugee camp in central Gaza, would be a mere $2 million (1.5 million euros) over three years, with an immediate investment of $200,000 needed before next winter's rains arrive.
So far, France has been the largest donor to the preservation efforts, giving 110,000 euros ($146,000) since 2010. UNESCO has contributed another $35,000.
"All the emergency safeguards that we've put in place -- corrugated iron fences, supports, sandbags -- are working but they are only temporary. And within a year, if we don't do anything, the worst is yet to come," Elter said.
The decaying remains cover 15,000 square metres (161,000 square feet), and the surrounding site stretches across 10 hectares (25 acres).
Situated among undulating sand dunes, the southern part of the complex includes a church and large crypt, a chapel, several baptismal fonts, living quarters and a refectory for the monks.
In the northern sector, there is an inn and bathing pools for the pilgrims who once visited.
Today, many of the sandbags that support the monastery's crumbling foundations are disintegrating because of the humidity. A blisteringly hot summer last year was followed by a very wet winter, which has left deep furrows in the soil.
Although there is a French stonemason who could do the necessary work to shore up walls in danger of collapsing, there are no funds to fly him over.
"The grass is beginning to destroy the mosaic floor," said Fadel al-Utol, a young Gazan archaeologist who looks after the site for the French-Palestinian preservation project.
"I need workers and weed killer to get rid of all this grass, I need to change 2,000 sandbags and I need wood to reinforce the platforms for visitors," he complains.
The team of workers who maintain the site have been underpaid for months.
And with no night watchmen, there are fears the site could be looted or damaged.
Meanwhile, it is used for training Palestinian experts who will be responsible for managing the archaeological sites and restoration of Gaza in 10 or 15 years time.
"We have a team there who are ready to work, who are able to manage this heritage," he says.
Every day, Utol takes groups of school children and students around the site, which had a record 1,880 visitors in March. He explains to them about the baptistry, the Romans, the pre-Byzantine Christians and the Ummayads in what is a unique educational experience in Gaza.
"The main aim of these visits is to get them out of the school routine. The second is to identify historical sites in order to better understand the history of Gaza and not forget that our ancestors left us a site to preserve," he says.
Saint Hilarion is not the only endangered archaeological site in the impoverished Gaza Strip.
In recent months, the Ezzedine al-Qassam Brigades, the armed wing of the ruling Hamas movement, took over Blakhiyeh in Gaza City, the site of the ancient Greek port of Anthedon, witnesses say.
And farther north, the area surrounding an ancient Byzantine church in Jabaliya, which is known for its mosaics of animals, was damaged during an Israeli bombing campaign in November.