The differences that once distinguished Hong Kong from the rest of China have become more blurred every year since the handover. Even the mention of a 'border' between the Special Administrative Region and Guangdong has become politically incorrect. Borders, after all, define international frontiers, not artificial divisions within the same nation. 'Boundary' is the preferred term, and marks a return to the past. It was the wording used up until the 1920s, and its use was even formalised. Until 1997, the perpetually busy Boundary Street in Kowloon marked what was - in purely legal terms - probably the world's strangest international frontier. As well as passing through the middle of one of the world's most densely crowded areas, Boundary Street marked the dividing line between British Kowloon, ceded 'in perpetuity' to Great Britain in 1860, and the New Territories, leased from China for 99 years in 1898. Following the second Anglo-Chinese war (1856-1860), variously known as the Arrow war or the second opium war, the Kowloon peninsula and Stonecutters Island were ceded to the British Crown in the Treaty of Tientsin, which ended hostilities. An arbitrary boundary line was drawn on a map across the northern section of the Kowloon peninsula - so straight that one suspects a ruler was run across a map - and a bamboo dividing fence with a gate was erected. This rudimentary international border divided 'British Kowloon' (south of the arbitrary boundary and legally part of the crown colony) from what was at that time a series of isolated village settlements whose inhabitants scratched a hand-to-mouth existence from their fields. Kowloon rapidly developed and prospered, as had Hong Kong Island before it, and expanded beyond the 'boundary' laid down in 1860. That part of the Chinese mainland immediately beyond British Kowloon became known as 'New Kowloon', and comprised modern Sham Shui Po, Lai Chi Kok and the environs of Kowloon City. An administrative no-man's land by the 1880s, free movement of people - and goods - was the norm. By the time the lease on what became the New Territories was signed in 1898, which moved the international frontier north to the Shum Chun River, the old dividing line was marked by a road named Boundary Street. British Kowloon then became known as Old Kowloon. As urban Kowloon expanded throughout the 20th century, the administrative border between ceded land and that granted in perpetuity gradually eroded. Construction of the Kowloon-Canton Railway in the early 20th century and substantial housing developments in Kowloon Tong in the 1920s meant the frontier defined by Boundary Street became meaningless to all except diplomats. Factory development around Sham Shui Po and elsewhere north of Boundary Street from the 20s further blurred the distinctions. By then, it was obvious that a British Hong Kong without the New Territories was economically and administratively - as well as politically - unviable, and the Kowloon boundary faded into one of history's curious quirks. During initial discussions about the future of Hong Kong in the late 70s, the old Kowloon boundary briefly came back into prominence. Percy Cradock, who as British ambassador was closely involved in the negotiations that led to the 1984 Joint Declaration, recalled in his memoirs, Experiences of China, that there was some (admittedly very tentative) cabinet-level discussion in Britain of resurrecting this original frontier. A discouraging complication, Cradock dryly noted, was the obvious need to have an immigration checkpoint at Prince Edward MTR station. Nevertheless, like East Berlin's Checkpoint Charlie in the cold war and the retention of Guantanamo Bay by the United States after Fidel Castro's takeover of Cuba, oddities of the past such as the Kowloon 'boundary' exert a fascination to later generations interested in the quirkier 'hows and whys' of local history. With Hong Kong's complete return to China in 1997, the only historical reminder of the former colony's mixed territorial status in Kowloon is in the name of the road itself, thundering with traffic at all hours.