'Esfahan nesf-e jahan ast,' goes the proverb - 'Esfahan is half the world'. That's how it was seen in the 16th century. London and Paris were upstart shanty towns compared with the architectural magnificence and spatial grace of Esfahan in what was then Persia. Although long ago eclipsed as a political and commercial centre, it still has plenty to offer. The question is whether 21st-century Esfahan can still pull the crowds. So far, so good. In 2005 there were two million overseas visitors to the country - a significant increase, but the city is still struggling to recover from the 33 per cent drop in 2003 caused by the invasion of neighbouring Iraq. Esfahan isn't just a collection of impressive buildings, although there are so many that the city has been described as a huge open-air museum. Iranian architecture is broadly divided into pre- and post-Islamic, dating from about the seventh century when the Arabs swept into the land, resulting in a stunning alchemy. The long history of Persian styles and subtleties, particularly from the Sassanian period, were brought to bear on Islamic principles. Art forms such as calligraphy, stucco work, mirror work and mosaics became closely with the architecture of the post-Islamic. Esfahan enjoyed its golden age under the Safavid empire during the 16th and 17th centuries, particularly under Shah Abbas I, (1587-1629) who unified Persia and made Esfahan his half of the world. The centerpiece of the city is Naqish-i Jahan square ('the image of the world'), an expansive rectangle of two-storey terraces enclosing fountains and lawns. To the north stands the Masjid-i Shah, or Shah Mosque (right), renamed the Imam Mosque after the revolution. It's the culmination of 1,000 years of mosque building with a stunning double shell dome. Its major entrance, the half-domed iwan, flanked by two minarets, is a pictorial signature of the city. Much of its beauty is a result of its seven-colour mosaic tiles and calligraphy. The city's most venerable mosque is the Masjid-al Jameh or Great Mosque. Built and rebuilt over 900 years, it's a time capsule of Iranian architecture, bringing together themes and ideas expressed elsewhere in the city. A secular expression of the Persian Islamic style is the Chehel Sotun palace, a royal retreat fronted by a magnificent verandah of 20 wooden columns, each 40 metres high, and reflected in a rectangular pool. This exquisite building, with its small throne room of reflecting glass and paintings of Safavid glories shows the Persian preference for garden settings and artistic understatement over bombast. The principles underpinning Islamic architecture are complex, but it has striking signatures clear to the eye: the massive domes with their proportion, form and roundness of span as the dominant elements; the tile work so densely intricate it could be painted (particularly the decorated ceilings of the Great Mosque); and the muqurnas, honeycombs in terracotta or tile cladding on the ceilings of the semi-domed iwans.