Sirkap and the Archaeological Complex of Taxila
Located about 22 kilometers to the west of capital of Pakistan, Islamabad, and about 25 kilometers to the northwest of the city of Rawalpindi, the archaeological complex at Taxila was at one time at the intersection of three great trade routes connecting India, Central Asia, and Western Asia. 
John HubertMarshall, Taxila : An Illustrated Account of Archaeological Excavations Carried Out at Taxila under the Orders of the Government of India between the Years 1913 and 1934, First Indian Reprint 1975 ed. (Varanasi: Bhartiya Publishing House, 1951), pp. 1-2.
Its urban form was developed in the late sixth century bce, and it flourished from the third century bce to the seventh century ce. Its decline can be linked to changes in the trade routes and a subsequent population decrease. 
For a concise chronology of the rulers and empires in Taxila, see Dani, The Historic City of Taxila, pp. 175-176.
It is a vast complex of monasteries, temples, and three separate cities which covers almost ten square kilometers. It was "discovered" by Alexander Cunningham in the late nineteenth century as he traveled throughout India following the pilgrimage routes of the Chinese monks Fa Xian, who traveled through the Indian subcontinent in the fifth century ce (404-414), and Xuan Zang, who did the same in the seventh century ce (630-644). 
Singh, The Discovery of Ancient India, pp. 36-39. For Alexander Cunningham's whole program and details of his years as the Director General of the Archaeological Survey of India, see Ibid., pp. 23-134.
While Cunningham did not engage in full excavations at Taxila, he did carry out some preliminary digs in and around the area. 
The most extensive archaeological data from Taxila published by Alexander Cunningham can be found scattered throughout his annual reports to the Archaeological Survey of India. See Alexander Cunningham, Four Reports Made During the Years, 1862-63-64-65, 2 vols. (Simla: Government Central Press, 1871), Alexander Cunningham, Report for the Year 1872-73, vol. 5, Archaeological Survey of India (Varanasi: Indological Bookhouse, 1875), and Alexander Cunningham, Report of a Tour in the Punjab in 1878-79, vol. XIV, Archæological Survey of India (Varanasi: Indological Bookhouse, 1882).
But it was the twentieth century British archaeologist Sir John Marshall who did the most extensive work there from 1913 to 1934. His finds were steadily published in his yearly Annual Reports, and in 1951 Marshall re-published his data in a three volume final report now known simply as Taxila. He wrote in his introduction, "in such an excavation there comes a time when the entire body of data has to be re-examined and coordinated, and a comprehensive account of the whole put at the service of archaeologists and historians." 
Marshall, Taxil, p. xvii.
Although there have been various small archaeological digs in the area since the 1951 publication of Taxila, Marshall’s work is by far the most comprehensive archaeological record of the site to date. 
Unfortunately, some 400 pages of Marshall’s original notes were lost during the Second World War, as he relates in his introduction, "[s]ome of these I was able to replace with the help of duplicates kept for safety’s sake at Taxila; others I could not replace, and have had to fall back occasionally on my memory" (Ibid., p. xviii). In regards to other digs, of note are some articles in the journal Pakistan Archaeology and the Journal of Central Asia, some parts of J. E. van Lohuizen-De Leeuw, The "Scythian" Period: An Approach to the History, Art, Epigraphy and Palaeography of North India from the 1st century B.C. to the 3rd century. A.D (Leiden: E.J. Brill, 1949), and a very good summary work Dani, The Historic City of Taxila, op cit. Most recently, there has been an ongoing excavation of parts of Taxila by a Korean team, but they have yet to put forth a full publication.
In Taxila Marshall identified three separate cities: the earliest, and smallest, was located on Bhir Mound which was the city inhabited by the Achaemenids.
Recently, J. Mark Kenoyer, "New Perspectives on the Mauryan and Kushana Periods," in Between the Empires: Society in India 300 BCE to 400 CE, ed. Patrick Olivelle (Oxford: Oxford University Press, 2006), p. 39 observes that "there is very little evidence for Achaemenid cultural influence in the layout of the site or the pottery." He suggests that these early layers have more in common with the indigenous culture Indus valley region itself.
This city had the first wave of Greeks, and was in decline by the end of Mauryan rule. In the late Mauryan period and during Indo-Greek rule, the population moved to Sirkap which soon came under control of both the Indo-Scythians and Indo-Parthians. With the arrival of the Kusanas, the city moved to Sirsukh which, unfortunately, has yet to be adequately excavated. 
It seems Sirsukh is closed to any excavation activities in the near future as in the last half century more and more dwellings have arisen to cover the site. Any excavation today would have to displace a large population.