Located by the Bluefish River, this 18th-century property has entered the market with contemporary updates. Allison Cayzer of Coldwell Banker Realty-Back Bay listed the mansion at 47 St. George St. in Duxbury — also known as “Riverlea” — for $4,650,000 on Dec. 9. The Colonial has six bedrooms, five full bathrooms, and one half bathroom in 4,600 square feet of living space. Riverlea was originally constructed in the 1700s by shipping mogul Samuel Frazer, according to the listing. A recent full renovation has introduced modern features, including central air and heating, gas fireplaces, and smart-home technology. The main event on the first floor is an open living, dining, and kitchen space with oak flooring and numerous windows overlooking the water. The adjoining porch also offers views of the river. This side of the home includes a mudroom and an office with exposed wood beams. On the other end is a suite with a bedroom, bath, eat-in kitchen, and a family room with a stone fireplace.