In 1162 Flathbert O'Brolchain, a successor to St Columba, and Muirchertach O'Loughlin, an Irish Chieftain, removed over 80 dwellings to build an earth wall (known as a cashel) around St Columba's abbey in Derry. This is one of the earliest recorded defensive fortifications in Ulster.
Ever since the reign of Queen Mary (1553-1558) the English had wanted to occupy and fortify Derry as they considered it the cornerstone of their conquest of Ulster. In September 1566 they finally achieved their aim when Colonel Edward Randolph, who commanded a military force under Queen Elizabeth's Lord Deputy Sir Henry Sidney, built the first English fortification of Derry. He expelled all the Irish inhabitants of the town and erected earthworks for the defence of the garrison. Randolph was destined to die a few months later when his forces clashed with those of Shane O'Neill, Earl of Tyrone, who was attempting to wipe out the garrison.
These first military defences encompassed the site of Derry's first cathedral, the Teampall Mór, built in 1164 near St Columba's original monastery. Today the Long Tower Church stands in the same area.
In April 1567 an accidental fire spread to the Teampall Mór which was being used as a magazine for gun powder, causing a great explosion. This destroyed the cathedral along with other church buildings and the soldiers' quarters. As a direct result, the English forces sailed back home - leaving Derry in ruins for many years.
In 1600 the English returned, still determined to gain firm control of the area by establishing a permanent garrison in Derry. Sir Henry Docwra was sent by Lord Deputy Mountjoy to occupy and fortify the town with a large force of men. His main task was to keep in check the Ulster Chieftains and try to get them to co-operate with the Crown. He landed virtually unopposed at Culmore on 16 May and, after fortifying the existing castle there, marched to Derry several days later. Docwra described his first view of the town in a report thus:

Old Derry was rightly likened to an island because in very early times the river Foyle had divided, east and west, around the central hill of the town. The western branch had flowed roughly along the line of the present-day Lecky Road and Rossville Street. By 1600, however, this branch of the river had virtually disappeared and most of the low-lying western area had turned to marsh.
Using locally scavenged materials and their own provisions, Docwra's men built two more forts. The lower one at the river's edge (constructed around the ruins of the old O'Doherty castle) was for the stores and the upper or great fort on the high ground above was for the soldiers' quarters and other housing. It was also to be used as the main retreat if under attack. These earthen defences and the large garrison of soldiers re-established a strong military presence in Derry.
Docwra's fortifications covered only half of the area later walled by the Irish Society of London. Most of it lay between the present-day St Augustine's Church and the grounds of the Long Tower Church, roughly the terrain first fortified by Colonel Randolph. A number of other dwellings were sited between the two forts on the slope of the hill.

Plan of Derry in 1603 showing Docwra’s completed fortifications and plans for further improvements.

To further the English intention of having Derry as a commercial port, as well as a defensive garrison, King James I granted its first Charter of Incorporation in 1604. In addition James also advocated the Walling of Derry but this was not undertaken for several years.
Docwra left Derry in 1606, leaving Sir George Paulettin command.Paulett was disliked by both the Irish and the English as he had no military experience and was ill-mannered with everyone. His gross mismanigement allowed the fortifications to deteriorate and his arrogant behaviour alienated Cahir O'Doherty, Chieftain of Inishowen. This resulted in O'Doherty using his secretly gained knowledge of the fortifications to attack and subdue the Culmorc garrison in April 1608. He went on to attack the Derry forts where Paulett was killed and the city was taken after two days of fighting.
O'Doherty's forces eventually departed the ransacked city a few weeks later, leaving only the battered ramparts of the Walls and church still standing. Once again Derry's defences had tumbled – this time at the hands of an enemy.
A contingent of soldiers under Captain John Vaughan recovered the city shortly after and rebuilt the forts and dwellings. The Lord Deputy, Chichester, imposcd a fine upon O'Doherty's followers in Inisliowen to pay for all the repairs.
So far, Derry's fortifications had followed a simple pattern. Their walls consisted of large mounds of earth and sods dug out of the ground leaving a deep trench. These mounds were transformed into basic defensive ramparts, sometimes reinforced with timber with parapets of earth, stone or wood fashioned on top. One or more gates with a drawbridge were built to control access to the fort. These fortifications would, of course, be weakened by the weather and constant use.
So the earthwork wall, if it was not constantly maintained, gave little protection to the population within. Consequently, whenever an attack was imminent, the local people preferred to flee to the countryside rather than defend the fort.
To restore the confidence of the population and greatly increase the strength of Derry’s defences, Chichester urged the Privy Council of the king to have the city ‘walled in stone’. He considered this to be the only way to prevent another disaster similar to the O'Doherty sacking. He also advised the king to annex a large area of Inishowen and grant parcels of land to loyal subjects. In return, these new landowners (known as Planters) would have to pay rent to the Crown and also maintain the proposed new Walls, castles and defences.
Chichester's strategy was simple; if the Planters invested time and money in landholdings given to them by a king they supported, then, if danger threatened, they would not flee as the local populace had done. Instead they would band together with the military forces behind the stoutly walled fortifications and defend their own territory against a common enemy. In 1608 Chichester petitioned the king to carry out his plans.