Cassiobury House, a seat of the Earls of Essex, lies a mile away from Watford, in Hertfordshire. It is an old mansion, but has been much altered from time to time. Cassivelaunus lived in the manor of Cassiobury, and the Abbot of St. Albans once numbered Cassiobury among his many religions houses. Some invaluable art treasures are preserved here, among them being paintings by Vandyke, Rubens, Reynolds, Lely, Romney, and Turner. The present Earl of Essex throws open to the public his delightful park, which extends over some six hundred acres. The trees are particularly fine some of them were planted in 1683 by Le Notre, the famous gardener to Louis XIV. Cassiobury House is an excellent specimen of "the stately homes of England."
source: The Queen's London : a Pictorial and Descriptive Record of the Streets, Buildings, Parks and Scenery of the Great Metropolis, 1896