Constitution island divides the bed of the Hudson unequally at the bend round the point, the western branch being a marshy shallow. This island, a mass of rock, was defended by batteries on a level with the water, and the glacis formed in the rock bade defiance to trenches. A heavy chain cramped into the rocks at either end, supported by buoys, stretched across the angle made by the river, and formed an effectual bar. This chain prevented the English from ascending the river in their armed ships, and the great object of the works on both sides was to protect it. Twenty pieces of heavy ordnance, discharging grape, menaced those who should attempt to cut a link, with destruction. And the roller on which the chain moved, suffered it to grow slack, thereby preventing any iron-beaked vessel from breaking it under the combined forces of wind and tide. As soon as the shock was thus broken, the chain could be immediately made tense, and the vessel must be turned aside and stranded on one or the other shore.
In The Hudson From the Wilderness to the Sea, Benson Lossing explains the origins of the original name of Constitution Island, Martelaer's Rock, probably a misspelling of the Dutch word Rach which was a sailing term for a specified distance:
"Between Cold Spring and West Point lies a huge rocky island, now connected to the main by a reedy marsh already referred to. It was called by the Dutch navigators Martelaers Island, and the reach in the river between it and Storm King, Martelaers Reach. The word martyr was used in this connection to signify contending or struggling, as vessels coming up the river with a fair wind would frequently find themselves, immediately after passing the point of the island into this reach, struggling with the wind right ahead."
An obvious strategic point of defense, a fort was begun on the island in 1775. The fort was named Fort Constitution in honor of the cause of the Revolution and the island was soon known as Constitution Island. The building of Fort Constitution was suspended while the militia concentrated their efforts on building Forts Clinton , Montgomery and Independence south of the island in the hope of containing the British further down. After those forts were taken by the British in 1777, the Americans decided to finish the fortifications at West Point and at Constitution Island. On the island two batteries were constructed on the western shore while redoubts on the higher land protected the lower forts.
In 1834 Susan and Anna Warner moved to Constitution Island with their father, Henry Warner. They intended to live on the island only during the summer but reverses in Henry Warner's fortune forces them to sell their home in New York City. In order to support themselves and their father, Susan and Anna Warner began to write novels. Susan Warner's first book, The Wide, Wide World was so popular both in the United States and abroad that soon she was producing at least one novel each year. Queechy and The Law and The Testimony were her next two books. The Hills of Shatemuc, her next novel sold 10,000 copies on the day it was published.
Anna Warner is best known for writing the words to Jesus Loves Me, This I Know. She worked with her older sister Susan on several books and published Dollars and Cents , a novel which relates the story of their change in circumstances. She also wrote a biography of Susan after her sister died.
Although their writing brought them fame, it never made them rich. They continued their days on the island, spending winters on the mainland at friend's houses, doing their own gardening and cooking. Gardening was one of Anna Warner's great joys; one of the books she published was called Gardening By Myself. The sisters promoted the somewhat radical idea that young ladies could actually do their own physical work such as gardening.
The Warner sisters were also known for their deep commitment to religious teachings. Each Sunday, they held Bible classes for cadets from West Point. After Susan's death in 1885, Anna continued the tradition.The sisters are buried at the West Point cemetery.
After Susan died, Anna was offered large sums of money by developers for Constitution Island. She refused to sell despite her continued poverty. Finally Mrs. Russell Sage, a noted philanthropist, bought the property and donated it to West Point in accordance with the wishes of the Warner sisters. A condition of the gift was that Anna Warner would be allowed to live at the island until her death. When she was unable to maintain the property, the cadets created The Constitution Island Association, which continues today to preserve the island and its historic sites. The Warner house is open to the public with guided tours by docent volunteers on certain weekends in the summer.