Possible Clues:

• New Hampshire city
• City on the Merrimack River
• City in New Hampshire
• 1955 Horse of the Year
• New Hampshire's 'Gate City'
• Second-largest city in New Hampshire
• City on the Merrimack
• Horse of the Year in 1955
• Seat of Hillsborough County, N.H.
• City ESE of Keene