Goverment and Law

It is clear that there had to be some sort of government and law that organized and ran the cities, though again, there is no specific or clear written evidence to support this. So how do we know? It seems incredibly unlikely that cities as highly organized as Harappa and Mohenjo-Daro would have been able to be constructed without some sort of governing organization to plan and then construct them. Without knowing their language, however, we are stuck at merely guessing what the government and law may have been like.