Lahore is the second largest city in Pakistan after Karachi. It is the cultural capital of Pakistan. It is an ancient urban centre. It was one of the major cities of the Mughals in the 17th century. Its location as an important crossroads in the northern Punjab brought riches as well as invading armies. As a result the city cultivated a rich architectural heritage that reflects the political fortunes of its conquerors. The modern city of Lahore, however, is organised along a pattern set mostly by the British during their approximately one hundred years of colonial rule over the Indian sub-continent. Today Lahore has almost seven million inhabitants plus innumerable migrant workers from the surrounding small villages. Its precarious location between the Ravi River to the West and North and the Indian border to the east forced the city to grow mostly southward. The Walled City of Lahore covers an area of 256 ha with a population of 200,000. The city walls were destroyed shortly after the British annexed the Punjab in 1849 and were replaced with gardens, some of which exist today. The Circular Road links the old city to the urban network. Access to the Walled City is still gained through the 13 ancient gates, or their emplacements. The convoluted and picturesque streets of the inner city remain almost intact but the rapid demolition and frequently illegal rebuilding, which is taking place throughout the city, is causing the historic fabric to be eroded and replaced by inferior constructions. Historic buildings are no exception and some have been encroached upon. The few old houses one can still see in the city are usually two or three storeys tall, with brick façades, flat roofs and richly carved wooden balconies and overhanging windows.