"Wheeler (1968, 3rd edition) proposed the following: It is, simply, this. Sometime during the second millennium B.C. – the middle of the millennium has been suggested, without serious support – Aryan-speaking peoples invaded the Land of Seven Rivers, the Punjab and its neighboring region. It has long been accepted that the tradition of this invasion is reflected in the older hymns of the Rigveda, the composi- tion of which is attributed to the second half of the millennium. In the Rigveda, the invasion constantly assumes the form of an onslaught upon walled cities of the aborigines. For these cities, the term used is pur, meaning a “rampart,” “fort,” “stronghold.” One is called “broad” ( prithvi) and “wide” (urvi). Sometimes strongholds are referred to metaphorically as “of metal” (dyasi). “Autumnal” (saradi) forts are also named: “this may refer to the forts in that season being occupied against the Aryan attacks or against inundations caused by overflowing rivers.” Forts “with a hundred walls” (satabhuji) are mentioned. The citadel may be of stone (afmanmayi): alternatively, the use of mud-bricks is perhaps alluded to by the epithet ama (raw, unbaked); Indra, the Aryan war-god is purandara, “fort-destroyer.” He shatters “ninety forts” for his Aryan protégé, Divodasa. The same forts are doubtless referred to where in other hymns he demolishes variously ninety-nine and a hundred “ancient castles” of the aboriginal leader Sambara. In brief, he renders “forts as age consumes garment.” If we reject the identification of the fortified citadels of the Harappans with those which the Aryans destroyed, we have to assume that, in the short interval which can, at the most, have intervened between the end of the Indus civilization and the first Aryan invasions, an unidentified but formidable civilization arose in the same region and presented an extensive fortified front to the invaders. It seems better, as the evidence stands, to accept the identification and to suppose that the Harappans of the Indus valley in their decadence, in or about the seventeenth century BC, fell before the advancing Aryans in such fashion as the Vedic hymns proclaim: Aryans who nevertheless, like other rude conquerors of a later date, were not too proud to learn a little from the conquered . . . (1968: 131–2)"