The City of Freetown, capital of Sierra Leone, sits on a narrow peninsula of land that juts sharply into the sea.
For close to two centuries - from 1787 to 1961 when this West African country was ruled by the British - the military strategy of the colonial rulers was quite straightforward: if your army was strong enough to hold the neck of the peninsula, you could hold the city.
But this simplistic piece of military logic depended on one crucial factor: having an army strong enough to hold that vital piece of land. At the moment, despite the presence of almost 9,000 UN peace-keepers in the city, Freetown appears to be lacking an army capable of doing that.
Sierra Leone is a country slipping ever deeper into despair and chaos. Last night, with the American and British authorities preparing to evacuate their citizens under military protection, terror was increasingly taking hold.
"The people here are panicking," one official source in Freetown told The Independent yesterday. "All day there had been the clatter of helicopters. The UN people themselves are panicking. The situation could go either way."
The source of the alarm is the latest twist in a bloody and terrifying civil war that has racked Sierra Leone for close to a decade.
At odds are the forces of the country's government, loyal to President Ahmed Tejan Kabbah, and the Revolutionary United Front (RUF) led by Foday Sankoh - a former army corporal and TV cameraman.
It was the RUF that deposed President Kabbah in a coup in 1997 - a situation eventually reversed by the Western-backed Ecomog forces, led by Nigeria, and the mercenaries, Sandline, led by Major Tim Spicer.
It was also the RUF - a murderous, machete-wielding force that has gang-raped and hacked off the limbs of hundreds of innocent citizens - which attacked Freetown in January 1999.
Seizing the poorer, western part of the city, it dug in and tried to again seize power before the Nigerian-led international force rallied and drove it out in a series of bloody confrontations. As the RUF withdrew, it systematically burnt entire city blocks, embassies, government buildings, churches and mosques.
In recent weeks, despite an apparent ceasefire agreed by Sankoh, RUF soldiers have again been marching on the capital.
The RUF, whose members know Sankoh affectionately as Papei (papa), is made up of Libyan-trained, pan-African revolutionaries and rank-and-file urban youths who turned to the the movement as a means to enrich themselves by looting the country's diamond mines. In the past seven days they have captured and held hostage up to 500 UN peace-keepers, including one British military adviser, and stolen weapons and armoured personnel carriers.
In one incident, the RUF took 13 armoured personnel carriers from a Zambian unit of 200 soldiers. It is on this UN hardware that the rebels have been advancing.
The UN peace-keepers, including soldiers from Kenya, Zambia, India and Nigeria, have tried to strike back. A source with the UN mission in Sierra Leone said there had been fierce fighting on Saturday. The source said the mission'sforces had used a helicopter gunship to try to halt the rebel advance. "We pounded them, we pounded them well," said the source.
But it has not been enough. Diplomats privately concede that the UN forces do not have adequate equipment and that some are poorly trained. One report says the Zambians who had their guns stolen apparently had no ammunition. In short they are no match for the bloody and battle-harden men of the RUF.
On Saturday, the sense of unease within Freetown was heightened when the UN reported that the rebels had secured the town of Hastings, which is just 13 miles from the centre of the capital.
But yesterday, the UN said this statement had been made in error and that the town was not in rebel hands. "The situation this morning is pretty static, that is, about the same as last night before we made our unfortunate error," said a spokesman, Philip Winslow.
"It is still believed that there are RUF rebels between Rogberi and Masiaka [towns 40 miles east of Freetown]. We had spotted a column of them with an unspecified number of vehicles, so we know they are there. But there is no immediate threat to Freetown."
Mistake or not, the situation is such that the British and Americans are no longer prepared to risk the situation. As Robin Cook, the Foreign Secretary, announced that all non-essential staff at the British High Commission were being evacuated, it was also announced that 700 paratroops had been scrambled to Dakar in nearby Senegal. These troops will oversee the evacuation of the 400-or-so British citizens in Sierra Leone if required.
"There is a deterioration in the security situation. We are feeling concerned," a Foreign Office spokesman said last night. "There has been no news on the British military adviser - the UN is still negotiating for his release."
Such negotiations yesterday led UN officials and representatives of the RUF to travel into the interior of the country, accompanied by Ali Tureiki, a special envoy sent by Colonel Gaddafi of Libya.
"The Libyan envoy, a joint [rebel/UN] mission and various other diplomats ... are going upcountry to the north, to Masiaka and the other places," said Mr Winslow.
Apart from the immediate concern about the hostages, Sierra Leone's descent into chaos presents a severe challenge for the UN and its secretary general, Kofi Annan.
After an "Africa month" in January at the UN, Britain and the United States tried to counter growing criticism that Africa did not receive the same attention as European crises, such as Kosovo. They did so by arguing for a greater peace-keeping mandate for the UN in Sierra Leone and the Congo
A seven-member mission, led by the American envoy Richard Holbrooke, is currently examining the prospects for deploying 5,500 UN peace-keepers to the Congo to monitor a ceasefire agreed in April. As they start their tour, Rwandan and Ugandan forces - which back rival rebel factions in Congo - have been fighting in the Congolese city of Kisangani.
One Africa observer, who has visited Sierra Leone many times, said last night: "In some ways this is make or break for Annan. His reputation is on the line, as is that of the UN operating in Africa. What chance is there for the Congo if they can't get this right?"
This will mean little to the people of Freetown. As they wait amid the growing panic - a murderous army descending upon them and getting stronger all the time - they can only hope that the soldiers protecting them can hold that crucial piece of land.