I want to know the answer to the following question:
What was used to fill a mill pond that became the Haymarket Square?
All the background I'm provided with is that "The largest reclamation efforts took place during the 19th century; beginning in 1807, the crown of Beacon Hill was used to fill in a 50-acre (20 ha) mill pond that later became the Haymarket Square area.". Is that enough to answer the question?
Answer: yes