The Carboniferous Limestone island rises to about 200 feet (61 m) and serves as a wind and wave break, sheltering the upper reaches of the Bristol Channel.

It is protected as a nature reserve and Site of Special Scientific Interest (SSSI) with a large bird population and plants including wild peonies.

In the 1860s the island was fortified with ten 7-inch rifled muzzle loaders as one of the Palmerston Forts for the coastal defence of the Bristol Channel until it was abandoned in 1898.

The infrastructure was reused in World War I and II when Mark VII 6-inch breech-loading guns and search lights were installed.

To enable the movement of materials, soldiers from the Indian Army Service Corps initially used mules and then installed a cable-operated winched switchback railway.

There are some folds and fractures with dip angles up to 75 degrees created during the final phases of the Variscan orogeny near the end of the Carboniferous Period, 300 million years ago.

[15] Steep Holm is protected as a nature reserve and Site of Special Scientific Interest (SSSI), notification having taken place in 1952.

[23][24][25] Alexanders (Smyrnium olusatrum) is also common along with golden samphire, buck's-horn plantain (Plantago coronopus) and wild leeks (Allium ampeloprasum).

[28] The earliest sign of human activity on the island are prehistoric vertebrae of red deer discovered in Five Johns' Cave during an exploration in 1975.

[21][31] Accurate exploration and interpretation of the site is difficult as it was reused by builders in both the Victorian era and during World War II.

[34] In addition to shards of cooking pots from the Roman era, some luxury items have been identified including Arretine ware, La Tène style brooches, and an amphora dating from between 90 and 140 AD which was made in southern Spain.

[35] Fragments of pottery roofing and box flue tiles have been identified signifying the presence of a heating system and possibly a bath house.

[41] The Vikings took refuge on Steep Holm during the summer of 914 and then carried out raids on the coast of Somerset at Watchet and Porlock, according to the Anglo-Saxon Chronicle.

[46] The island seems to have been held, in association with the local manors of Uphill and Christon, by the Bek family, who granted it to Henry de Lacy, 3rd Earl of Lincoln.

[48][49][50] By 1453 the overlordship of the island was held by James Butler, 5th Earl of Ormond, and in 1460 the advowson was exercised by Margaret Talbot, Countess of Shrewsbury.

On the opposing side of dispute were the descendants of the aforementioned Elizabeth Berkeley (James' the 1st Baron's, 1st cousin) and in particular through her daughter Margaret (de Beauchamp) that shows some curious tangled sub-plots.

It brought him into direct opposition with Sir William de Berkeley (2nd Baron and son of James Berkeley and came to a full head at the Battle of Nibley Green (1470), following what is described as Thomas Talbot's impetuous challenge to Sir William, which had concluded by the end of the following day with the death of Thomas Talbot and the subsequent sacking of his Manor at Wotton-under-Edge.

The Seymour descendants recovered the estates, owning them into the 17th century, although the only activity on Steep Holm seems to have been the employment of gull watchers and fishermen.

[52] In 1684 the Norton Beauchamp estate (possibly in Kewstoke, Somerset, near Sand Bay, north of Weston-Super-Mare) was sold to Edward Ryder.

It appears to have been auctioned by decree of the Court of Chancery 11 years later in 1695, possibly because of difficulties in maintaining sea defenses along the Somerset coast; however, this seems to have been disputed in the light of outstanding mortgages.

[53] Freke's granddaughter married into the family of John Willes, who was Chief Justice of the Court of Common Pleas and Member of Parliament.

They form part of a line of defences, known as Palmerston Forts, built across the channel to protect the approaches to Bristol and Cardiff.

[62][63][64][65][66][67] The facilities installed included a master-gunners house, a small inn, and a water tank holding 49,000 imperial gallons (220,000 L; 59,000 US gal) of rainwater.

[76] In 1927 the first test of the RAE Larynx (from "Long Range Gun with Lynx engine") an early pilotless aircraft, to be used as a guided anti-ship weapon, took place just off Steep Holm.

In 1940 and 1941 the battery was refortified by soldiers from the Indian Army Service Corps using mules to transport guns and equipment up the steep cliffs.

[81] Engineers from the Royal Pioneer Corps improved the infrastructure including importing sheep to feed the soldiers and, after a case of typhoid fever, shipping drinking water from south Wales.

This was linked to the plateau with a cable-operated winched switchback railway using prefabricated 60 centimetres (24 in) gauge lines which had been captured from the Germans in World War I.