I started out to investigate the Blockhouse and The Clarendon as two separate, neighbouring buildings of historical interest. Research soon revealed that both these buildings share an interwoven history, so it makes sense to present them together. In Medieval times there were no comprehensive arrangements in place for river defences on the Thames. There were some unconnected local or private defences, such as at East Tilbury and Cooling. Otherwise defence depended on an ad-hoc system of lookouts and beacons, and the hope that suitable military forces could be mustered in time if a threat was spotted. The weakness of this system was amply demonstrated in 1380, when a French fleet landed troops to sack Gravesend and Tilbury. Defending The River During the reign of Henry VIII a better planned and coordinated system of defences was established. The Gravesend Blockhouse, built in 1539/40, was part of this. Two other blockhouses were sited at Milton and Tilbury to provide an inner line of defence, and two at East Tilbury and Higham to provide an outer line. The blockhouses were arranged so that their cross fire would protect the whole width of the river, to enable them to stop ships, protect the upper and lower ferry crossings, and prevent troops landing. Construction An estimate from 1539 gives the cost of Gravesend Blockhouse as £211 13s 4d, and includes costs for 150,000 bricks, 200 tons of chalk and a large quantity of timber. It is thought the chalk was needed both for stabilising the water-logged site on which the blockhouse was built, and infilling for the walls. The walls were 6ft 9in (1.95m) thick, consisting of inner and outer skins of red brick, with chalk concretion in between. The blockhouse was a D shaped two-storey brick structure with an armament of 21 guns of various designs. There were covered gun ports in the semi- circular front, and out in the open on the roof behind a curved parapet. Other guns were mounted behind an earthen rampart extending both sides along the riverbank. The blockhouse also probably stored gunpowder, and kept a supply of bows, arrows, crossbows, pikes etc for defence against a landing party. The illustration below is Tilbury Blockhouse in 1588. It is thought the same basic design was used for Gravesend and the other blockhouses. Garrison The garrison consisted of a commander, his deputy, six gunners, two soldiers and a porter. The garrison members had other part-time occupations, which must have been needed because their pay from the Exchequer was often delayed for months, even years. Dereliction As part of defence cuts in 1553 the Thames blockhouses were disarmed. Milton and Higham blockhouses were demolished, East Tilbury was abandoned, while Gravesend and Tilbury were retained but allowed to decay. Reinstatement In 1588, with the threat of invasion by Spain, the Gravesend and Tilbury blockhouses were in a ruinous state. They were hurriedly repaired and re- armed; Tilbury Blockhouse was enclosed in star-shaped ramparts, and there is evidence, though it is not conclusive, that the same was done at Gravesend Blockhouse. The new defences also included an 800 yard (738m) boom between the two blockhouses, constructed of a line of boats linked by cables and reinforced by spars driven into the river bed. The contemporary illustration below shows the boom defence and the newly fortified blockhouses. The Spanish Armada’s failed invasion gave England a chance to continue unfinished work on the Gravesend and Tilbury blockhouses, in expectation that Spain would rebuild her fleet. But when the threat had passed, the blockhouses were again allowed to fall into disrepair, so that by the time of the next Spanish invasion scare they were again in poor condition. Other uses After 1600, Spanish invasion was no longer a threat, and the Gravesend blockhouse was assigned to the Customs Service, examining ships for dutiable cargoes, goods intended to supply unfriendly states, or for spies from those states. However, it had still not been maintained – by 1630 it was in a parlous state of repair, and the commander and garrison had not been paid for six years (two gunners died before receiving their pay). A document from 1631 provides an audit of the blockhouse’s facilities, and recommends construction of a watch tower and guard room above the existing structure. By the time of the English Civil War (1642–49) the blockhouse was used for storage of muskets. Civil War At the start of the war, Parliament gained control of the blockhouses. This was crucial because the King, Charles I, declared his intention to capture London by attacking from the Thames. The blockhouse garrison was now also tasked with arresting those suspected of being spies or plotters. The Embryonic Clarendon The monarchy was restored in 1660. In 1665 Charles II had a residence built behind the blockhouse for the use of the Duke of York (later King James II) as Lord High Admiral. The front of the building was decorated with an anchor and the date 1665. How often it was occupied by the Duke of York is unknown. Charles II entertained important guests there or in the blockhouse. The residence later became the Ordnance Storekeeper’s Quarters. In much altered and extended state, and now separated from the remains of the blockhouse by a road, the residence is now the Clarendon Hotel. The present- day road and pavement are helpfully adorned with studs detailing the outline of the blockhouse structure over which they are built. The sketch below is from the 1660s, and shows the blockhouse from the west (a companion sketch shows the view from the east). It shows the original structure of the blockhouse, the watchtower proposed in 1631, and the Duke of York’s residence. The latter appears to be a three-storey brick structure with tall chimney stacks characteristic of the period. The illustration below shows the entrance to the Duke of York’s residence. Dutch Raid of 1667 When the Dutch fleet was spotted on 9th June, both Gravesend and Tilbury blockhouses were again quite unprepared for action. The population of Gravesend panicked and began to leave, so it was impossible to muster volunteers to man the defences. In fact, the Dutch were unaware of the unpreparedness of the Thames defences, and focused on destroying and capturing naval assets in the Medway. This allowed time to reinforce the Thames defences, re-arm the blockhouses, and build a new battery called Trinity Fort to the east of Gravesend Blockhouse. Quiet Years Following the Dutch raid, it was decided to build a powerful new fort with barracks at Tilbury, the blockhouse there being converted to a magazine. Gravesend Blockhouse was left to perform only a subsidiary role. It continued to carry out Customs duties – the Governor of the blockhouse, Sir John Griffith, was sacked in 1669 for illegally demanding tolls from ships cleared by Customs searchers. It also had a ceremonial role when important visitors arrived by ship at Gravesend. In 1701 the blockhouse’s armaments were recorded as ”about 20 guns planted level with the water”. The garrison consisted of a sergeant and twenty soldiers. It is unclear whether they were quartered in the blockhouse, the storekeeper’s quarters (now the Clarendon) or in local billets. By 1715, the blockhouse had been extended with a V-shaped addition to the rear, and a semi-circular western flank, all surrounded by a timber stockade with a south-facing opening to the storekeeper’s quarters. New internal walls and a pitched roof were also added, and to the east there were stables and a dog house. At some later date the watchtower to the rear was removed. The large capacity of the magazine at this time was considerably in excess of requirements for the blockhouse’s own guns, so it is thought it was being used as a storage depot for gunpowder to be used elsewhere. The plan below shows the layout of these buildings in 1715. The illustration below shows a panoramic view of Gravesend and the blockhouse in 1734. A report of 1766 states that the batteries, magazine, buildings and wharfing are in good order. The armament by this time consisted of only ten guns, quite inadequate for any serious military need, and feeble in comparison with the powerful riverside guns at Tilbury Fort. Threat From France During the American Revolution, France allied with the American Congress in revolt against the British. As a result Britain feared invasion by France, and England’s coastline and rivers were examined for vulnerability. At Gravesend, a replacement of the blockhouse gun positions on the riverbank was recommended by Captain Hyde Page, who also conceived a design for a new fort to the east, around New Tavern Inn, to become New Tavern Fort. The blockhouse’s new gun placements would extend further east, ending only 38 yards (35m) from the new fort building. These works were started in 1780. The plan was now that New Tavern Fort would provide powerful long-range fire downstream as well as cross-fire with Tilbury Fort. The role of the blockhouse was to provide broadside fire against any enemy ships that got through the defences provided by the forts, and to protect New Tavern Fort from any reverse fire from these ships. During peacetime it was standard practice to dismount the guns and place them under cover for protection. In 1784 the old stables were used to store guns, carriages and shot. Napoleonic Wars During the Napoleonic wars (1803-15) further improvements were carried out to the blockhouse and fort. A statement of lands dated 1811 listed a number of stores and outbuildings.