Languard Fort, sited on Landguard Point, dominates the navigable channel on the north bank of the River Orwell estuary. In conjunction with Harwich Redoubt on the southern bank, this fort provided necessary protection for the strategic natural harbour. As the most important safe haven for shipping between the River Humber and River Thames, it is no surprise that numerous fortifications have been built here over the centuries. The first recorded structure was during the reign of Henry VIII in 1543, but what can be seen today comes from two phases of building in 1744 and 1871.

In 1744, John Peter Desmaretz designed a new fort, built in the shape of a pentagon with a large diamond shaped bastion at each corner. The entire structure was then protected by a first line of defence comprising a Glacis - an earthen rampart built as a low inclined slope with protected walkways along the top for a soldier to fire from. In effect, a Glacis was an artificial hill surrounding the fort, allowing the creation of a dry moat behind it. In 1753 Beauclerk's Battery was built out from the Glacis and covered way at the south west bastion, thus increasing the firepower across the harbour entrance.

With the addition of further earthworks during the 1780s, the whole of Landguard Point became a fortified camp, including the King's Lines and Prince's Lines, as well as North Redoubt, South Redoubt and Rainham Redoubt. The rationale behind this work was to create a fortified area from which a land-based force could safely operate.

By 1871 much of Landgaurd Fort's artillery was obsolete, and major re-modelling of the fort was required to facilitate new rifle muzzle loading (RML) heavy guns. To achieve this, the west bastion and associated curtain walls were removed and replaced with a curved curtain wall extending from Harwich Bastion to King's Bastion. This section was then protected by a Carponier, which projected out from the centre of the new curtain wall allowing flanking fire along the entire length of dry moat. The new curved battery contained seven casemates on its upper level, which housed 4 x 10 inch (250mm) RML guns and 3 x 12.5 (312mm) inch RML guns, each being served via hoists from magazines located directly below.

The seaward facing bastions (King's and Holland) were reinforced, and equipped with casemated 10 inch RML guns, and a 12.5 inch RML gun casemated in the curtain wall between them. The landward facing bastions (Harwich and Chapel) had Barbette mounted 9 (225mm) inch RML guns, and 2 x 8 inch (200mm) RML howitzers mounted on the curtain wall between them.

All the internal accommodation of Landgaurd Fort was also demolished during this building phase, with a new semi-circular block being built behind the new curved battery. This in effect split the central parade area in two but, in doing so, also created an inner defensive position to which soldiers could retreat should a landward attack breach the original 18th century defences. In 1878 a submarine mining establishment was cut into the Glacis between Harwich and Chapel bastions, effectively creating a triangular block (known as a Ravelin) from which the minefields protecting Harwich were controlled.

Towards the end of the 19th century, Landguard Fort was reaching the end of its useful life and, as a consequence, three new batteries were constructed outside of the fort called North, South and Darnell's (named after the fort's captain who successfully repelled a Dutch attack in 1667). Landguard Fort was manned during both world wars in an anti-aircraft role, but its working life finally came to an end in 1956 when coastal artillery was disbanded.