Explanation: The Indus Valley Civilization, which flourished around 2600 BCE to 1900 BCE, is renowned for its advanced urban planning and sophisticated infrastructure, particularly in the areas of sanitation and drainage. The cities of Harappa and Mohenjo-Daro are prime examples of this civilization's engineering prowess.
One of the most notable features of these ancient cities was their complex drainage systems. These systems were designed to maintain hygiene and prevent the spread of diseases. The drainage systems included covered drains running along the streets, which were made of bricks and were designed to carry waste water away from the living areas. Additionally, each house in these cities had its own private toilet connected to the main drainage system, ensuring that waste was properly disposed of and did not contaminate the living spaces.
The drainage systems were not just limited to the streets. They also included soak pits, which were used to filter and dispose of waste water. These soak pits were designed to allow the water to seep into the ground, thereby preventing the accumulation of stagnant water that could have led to the breeding of mosquitoes and other disease vectors.
The presence of these advanced drainage systems is a testament to the urban planning and engineering skills of the Indus Valley Civilization. They understood the importance of sanitation in maintaining public health and preventing the spread of diseases. This is why the correct answer is that the cities were sanitary because they had complex drainage systems.
It is important to note that while other factors such as the presence of soldiers, emperors, and large markets were significant in the functioning of these cities, they did not directly contribute to the sanitation of the cities. The role of soldiers was primarily in maintaining law and order, while emperors were responsible for governance. Large markets were important for trade and commerce but did not play a direct role in sanitation.
In conclusion, the advanced drainage systems of the Indus Valley Civilization were a key factor in maintaining the sanitation of their cities, making them some of the most hygienic urban centers of their time.