My first sight of Africa's highest summit is from an aircraft window, on the short flight from Nairobi, in Kenya, across the border to Tanzania. The mountain looks imposing - a giant humpbacked whale breasting a sea of clouds - and for a moment the prospect of me standing on top seems an improbable fantasy.

When the climb begins two days later, I quickly learn the word " pole", meaning "slowly". My guide's constant refrain of " pole, pole" is good advice; beetling up the rocky slopes of the mountain, which is as awe-inspiring from below as it is from above, would only invite trouble.

"POLE, POLE" ALSO APTLY describes Arusha, at the foot of Meru Mountain, where many Kilimanjaro climbers base themselves. Meru may be a smaller mountain than her cousin 50km away but she is a more technical climb and looms over the town, casting afternoon shadows across the small collection of shops and houses and the dirt square bus station, from where travellers make their way south to Dar es Salaam, east to Kenya and north to Lake Victoria and the jungles of Uganda.

The town has a languid charm; locals sit outside bars drinking Tusker beer as the spring sunshine filters through the delicate purple flowers of the jacaranda trees that line every street. Most of Arusha's trade and bustle belongs in the colourful market but even here there is a relaxed air, traders sitting beside neatly stacked pallets of colourful vegetables and enormous avocados.

The fruit and vegetable market is run by a women's co-operative and the clothes and head scarves of its members are as brightly coloured and attractive as the produce on their wooden trestles. Elsewhere, in the male-dominated general goods market, the trade is more cut and thrust but even here, when I inquire about the price of a Tanzanian football shirt, the bargaining is good-humoured. I ask if Tanzania are a good team and the salesman says they "are better than Malawi but not as good as Zambia", leaving me none the wiser.

Arusha might be a typical East African town - its middle-of-a-roundabout clock tower boasts of being halfway between Cairo and Cape Town - but there is nothing typical about the mountain nearby, Kilimanjaro being a more potent symbol of Africa by far.

There is a palpable sense of expectation, mixed with a little unease, at the entry gate to the Kilimanjaro National Park. Nervous hikers clutching poles and being instructed in the art of " pole, pole" line up alongside porters shuffling impatiently from foot to foot as they await the opportunity to carry bags.

There is a strict system of regulation on the mountain and where once porters were permitted to carry 30kg or more, now there is a set of rules painted neatly on a tin-plated sign by the whitewashed ranger hut that states a maximum 20kg load. Strict censure awaits any porter who breaks this rule, which provides work for a greater number and allows for a more comfortable climb, although 20kg is still a significant load balanced on the head, which is the preferred method of luggage conveyance in this part of the world. Porters are also required to wear adequate footwear - trekking operators in Nepal and India could learn a thing or two from Tanzania about the humane treatment of load carriers.

No matter how heavy the load or how awkwardly a stove, a tent or dozens of eggs are perched on a porter's head, they are all faster than me. The Kilimanjaro path is not difficult at first but it is not long until I begin to feel the breathless effects of altitude.

Kilimanjaro is the world's largest freestanding mountain, surrounded by vast plains, and is so big it has its own ecosystem, with distinct flora and weather. I ask my guide, Kefas, what the weather will be like later and he says it is impossible to tell; the mountain will decide.

As it turns out, the (October) weather is stable throughout the six-day climb; cloudless and bright each morning until 11am, when massive cumulus clouds sweep in from the Serengeti Plains and consume the mountain and the valley below in great wet blankets. The clouds always clear promptly and with surprising speed during the late afternoon, leaving the evening bathed in the fiery glow of an East African sunset and the nights cold and crisp beneath a curtain of stars.

Spring in Tanzania is called the "small rain". The "big rain" arrives in the summer months of December and January, when few people want to climb. The really big rain falls in the autumn months of March and April and the best time to climb is in winter, when the weather is dry and bright, although cold on the summit.

The climb is punctuated by camps, each colder than the last. The nature of each camp is different because the climber ascends through very distinct bands of vegetation; equatorial forest gives way to scrubby moorland and, eventually, the horizon is filled with a high-altitude wilderness of boulders and black volcanic soil that coats boots and stings faces when the wind blows it in handfuls through the rarefied air. From the trees at the first camp, at Machame, come the unfamiliar squawks of African birds; the second camp, on the Shira plateau, is barren and desolate; and by the time we reach camp three, at Barranco, we might as well be on the moon rather than in Africa.

The key camp is at Barafu, at 4,673 metres, because it is from here that climbers make their attempt on Uhuru Peak, which is on the rim of the mountain's Kibo crater and rises to an intimidating 5,895 metres. We wake at midnight, head torches piercing the freezing night. Kefas hardly needs to remind me to step " pole, pole" because there is no other choice this far above the sea.

There begins a gruelling six-hour plod on steep slopes to Stella Point, on the rim of the volcanic crater near Uhuru. This part of the climb is notoriously tough and I keep my mind sharp by watching the dancing torch beams of climbers above and below and by examining the layers and layers of stars in the sky.

We climb the last of the steep slopes just as the first fingers of dawn push above the horizon. Kefas and I embrace and sit down heavily on the black earth and cold stones of Stella Point (at 5,739 metres). I know at last, as the sky turns a startling blue, that I will make it to the summit I saw below the wingtip of my plane.

The last hour of the climb is an easy stroll across a lava field. We pass several blindingly white glaciers as tall as village houses; it's hard to believe these will have fallen victim to global warming within 50 years.

My pace and my heart quicken as I see the summit sign and discover that the view from the top is hardly like that from a mountain at all. Kilimanjaro is so high and so far above the surrounding plains and clouds in the Rift Valley that it feels as though I am looking through the window of an aeroplane again.

Then I look up, and vapour trails high in the sky remind me that I am now part of someone else's view.