Answer the following question: I know that the answer to the question "What damaged the main city of Punjab?" is in "Punjab during Mahabharata times was known as Panchanada. Punjab was part of the Indus Valley Civilization, more than 4000 years ago. The main site in Punjab was the city of Harrapa. The Indus Valley Civilization spanned much of what is today Pakistan and eventually evolved into the Indo-Aryan civilisation. The Vedic civilisation flourished along the length of the Indus River. This civilisation shaped subsequent cultures in South Asia and Afghanistan. Although the archaeological site at Harappa was partially damaged in 1857 when engineers constructing the Lahore-Multan railroad used brick from the Harappa ruins for track ballast, an abundance of artefacts have nevertheless been found. Punjab was part of the great ancient empires including the Gandhara Mahajanapadas, Achaemenids, Macedonians, Mauryas, Kushans, Guptas, and Hindu Shahi. It also comprised the Gujar empire for a period of time, otherwise known as the Gurjara-Pratihara empire. Agriculture flourished and trading cities (such as Multan and Lahore) grew in wealth.". Can you tell me what it is?
Answer:
engineers