Knowledge of this fact has made it possible, where towers still exist, to determine without excavation the approximate sites of lost churches that once stood nearby.
The buildings still stand today because their round shape is gale-resistant and the section of the tower underneath the entrance is packed with soil and stones.
Famous examples are to be found at Devenish Island, and Glendalough, while that at Clondalkin is the only round tower in Ireland to still retain its original cap.
The round tower at Ardmore, County Waterford, believed to be the latest built in Ireland (c. 12th century), has the unique feature of three string courses around the exterior.
The Irish word[4][5] for round tower, cloigtheach, literally meaning bellhouse indicates this, as noted by George Petrie in 1845.
UCD Professor of Archaeology Tadhg O'Keeffe[6] has suggested that the towers were originally high-status royal chapels, citing how two of them (Kells and Duleek) were scenes of regicide.
[8] The oldest reference to a round tower (the one at Slane, see below) records its use as a refuge – however in this case it was burnt by the Vikings, killing everyone inside.
[9] At St. Ita's Hospital in Portrane, County Dublin, there is a replica round tower built in 1844 as a memorial to George Hampden Evans by his wife.
In 2003 Tony Ryan, a native of Thurles, County Tipperary, built a round tower at his Castleton Lyons Stud in Kentucky.
Brain Lalor states that fragments of the tower have been found on-site and its location is marked on OSI maps from c. 1850.
995/6 "Ard-Macha was burned by lightning, both houses damhlaig and cloigteach and fidnad" – Annals of Tigernach 1020 "Ard-Macha was burned with all the fort....and the Cloicteach, with its bells" – Annals of the Four Masters 1121 "A great wind storm happened in December of this year, which knocked off the conical cap of the cloicteach of Ard-Macha"- Annals of the Four Masters The tower is said to have stood 12 m north of the present cathedral (based on a map drawn in 1886 during the restoration of the cathedral) and possibly finally met its demise in 1642 when the town and cathedral were burned by Phelim O'Neill No trace of the tower remains.
A painting by Charles Lilly from 1790 and a print from 1789 show the round tower with a broken top standing to the south-west corner of the cathedral next to St. Patrick's grave.
No trace of the tower now remains but the site is pointed out next St Patrick's grave on raised ground which Barrow speculates may conceal its foundations.
Barrow states that Petrie in his notes (c. 1830s) quotes old locals describing the tower as of rude construction of large stones c.70 ft high with two windows at the top.
A Topographical Dictionary of Ireland[24] states "One of the ancient round towers stood here till 1807 when it was pulled down to make room for the belfry of the church".
The tower measured 105 feet long on the ground after being felled and apparently remained largely intact in its tubular form.
Keane[27] says: The ruins of a Round Tower to the height of eight feet and without door or window are said to have stood at Rath until the year 1838 when the materials were removed for the building of the Churchyard wall .
Barrow speculates that it is more likely that the tower and indeed the entire monastery at Dysart was built to replace the one that had been ruined at Rath Blamaic.
Barrow also states that when he examined the cemetery wall, in 1974, at Rath Blamaic that many of its stones looked likely to have come from the remains of the round tower.
Barrow states that the Silver seal of the dean and chapter of Ross, made in 1661, was embossed with a round tower which had a bulge at its base like Clondalkin.
Barrow states that Brash, however, upon visiting the area in 1852 and speaking with its oldest inhabitants was unable to find anyone with knowledge of the tower.
O'Donovan also records speaking to a local person born in 1750 who claimed to remember the tower standing as late as 1757.
John O'Donovan[23] identifies the site as Tullamaine, a parish whose overgrown closed cemetery is in a field about 4 km West of Callan.