This must be one of the longest city streets in the world. I measured it on my Tehran map with a ruler at about 14 kilometres, running from the railway station downtown to Tajrish square in the richer northern suburbs. Apparently it was built to improve military communications between the centre of Tehran and the royal palaces uptown - modern traffic has put paid to that idea, leaving the tree-sheltered, shop-lined, traffic-clogged street so beloved of Tehranis today.



Walking the length of it was always an appealing idea. It felt a bit like trying to capture something of what Tehran means by cutting a straight line through its varied neighbourhoods. The city topography is easy: north is up, south is down. Chronologically, socially and financially the same is largely - but not always - true. Tori Egherman and I decided to walk up. The joobs, deep roadside gutters, were flowing slowly with melt water from the mountains above, carrying the filth of rich people to the older, poorer bowels of the city.



Around the train station you can feel the hardship. As we looked for camera batteries an old man walked past with a polio-crippled leg, puffing the last embers of a cigarette stub. The shops sold overalls and hardware. A long line of people queued outside a warehouse for subsidised food. Every woman wore a chador. Trade down here goes by neighbourhood. A few motorbike shops all close together. Shoe shops further up, with sports and camping shops. Then medical supplies. Tori and I agreed it is good to know where these places are.



A man had returned from Canada and accosted us somewhere south of Jomhuri St. He wanted to talk politics. "If the Americans attack, we will be ready," he said. People were stooping as they passed to pick dates and sweets from a tray, which is often laid out in the street by a bereaved family after a death (above). A few streets up, baseball, American football and basketball paraphernalia was on sale in the sports shopes. Tori befriended the men in a juice shop. They were traditional, open and sports-mad.



The most unexpected discovery was a stamp shop. The collection had been passed down for two generations and the shop was now run by a young man (above) who had let his little finger nails grow very long in an old fashioned affectation signifying he does no manual labour. He had stamps from the South Arabian sultanate of Hadramawt - which was absorbed into communist south Yemen in the 60s. He also had bank orders for tomans from the 1920s, printed in New Malden in Surrey, close to where I grew up, and payable only in certain Iranian cities. They bore the sumptious whiskers of Nassereddin Shah.



The oriental planes start at Neauphle le Chateau St, named for Khomeini's place of exile in France. It is the high boughs of these trees that give Vali Asr such a distinctive feel, sheltering the street from the sun in summer and the rain and snow in winter. They continue all the way to Tajrish, past Vali Asr crossroads (with Enqelab St), Vali Asr Square, Vanak Square and Parkway junction. Tori's husband Kamran (above, who despite not coming on the walk insists he's not lazy) took us to lunch at Vali Asr Square. There are good restaurants further up the road - Hani's cafeteria opposite Fatemi St is probably the best.



The shops are more expensive as you head up the hill - but not necessarily better. There are also more parks (the terraced sides of Park Saiee are very pretty), more places to eat and drink, and a greater sense of leisure. The murals improve too. Some show stylised scenes from old stories. More revolutionary ones show martyrs and the face of Khomeini - glimpsed here in an old picture just inside a doorway. The large mural at the junction with Mirdamad St shows war martyrs from the religious minorities, their names written in Hebrew and Armenian.



But in Park Mellat a little further up, most attention is given to a man walking a little Pekinese dog, abhored by the religious authorities but cooed at by almost every couple walking in the park. I suppose some things just defy legislation.