Description from record TR 37 SE 39:
(TR 35927087) The Grotto [NAT] (1) The Grotto, Grotto Hill, Grade I. Many theories have been advanced for the origin of Margate Grotto, including Phoenician origin or a Roman Mithraic Temple. The Grotto was discovered in 1835 by a schoolmaster and his sons digging their back garden. It is however most likely to be early C19 as there are traces of a modern brick in one of the Gothic shaped arches. The pattern of the Grotto is 2 semi-circular passages leading to a central dome and then a passage leading off to a rectangular chamber. The Grotto has about 2000 square yards of shell mosaic consisting of 23 different types of shells, many of which are foreign. The cement which adheres the shells to the chalk walls is very similar to Roman cement and is said to contain fish oil and crushed shells. The motifs include common Egyptian, Greek and Indian motifs. In the rectangular chamber are motifs of the rising sun, the moon and stars. The modern buildings at ground level are not listable. (2)

Grotto Hill, a subterranean Grotto, chambers carved out of the solid chalk, two circular ones and a square at the end, linked by serpentine passages, all covered with shells in patterns, floral and geometrical. It is generally believed to be of great antiquity, but most probably dates from c1800. (3) Grotto, first discovered in 1835, by what seems to have been accidental discovery in the grounds of a school by the master's son. It is decorated with shells internally forming panels of flower-like and more abstract designs. Bomb damaged at one end. (4) A shell from a mosaic underground temple in Thanet was dated to AD 1670 +/- 100 by C14 dating. (5-6)

The following text is from the original listed building designation:
GROTTO HILL 1 1380 The Grotto TR 3570 NE 6/169 I
2. Many theories have been advanced for the origin of the Margate Grotto, including Phoenician origin or a Roman Mithraic Temple. The Grotto was discovered in 1835 by a schoolmaster and his sons digging their back garden. It is however most likely to be early C19 as there are traces of a modern brick in one of the Gothic shaped arches. The pattern of the Grotto is 2 semicircular passages leading to a central dome and then a passage leading off to a rectangular chamber. The Grotto has about 2000 square yards of shell mosaic consisting of 28 different types of shells, many of which are foreign. The cement which adheres the shells to the chalk walls is very similar to Roman cement and is said to contain fish oil and crushed shells. The motifs include common Egyptian, Greek and Indian motifs. In the rectangular chamber are motifs of the rising sun, the moon and stars. The modern buildings at ground level are not listable.
Listing NGR: TR3593270870 (8)


In 2005 Kent Underground Research Group carried out an assessment of the grotto. It is thought that the site originated as a dene hole, which could date from the Roman period up to the beginning of the 14th century. The reworking of the site, its expansion and decoration, could date from the 17th century onwards, though an 18th century date was felt more likely. (7)

<1> OS 1:2500 1955 (OS Card Reference). SKE48198.

<2> DOE(HHR) Dist of Margate B, Kent Feb 1973 30 (OS Card Reference). SKE40983.

<3> Historic Margate 1965 (GE Clarke) (OS Card Reference). SKE44081.

<4> The Bldgs of Eng NE and E Kent 1983 387-8 (J Newman) (OS Card Reference). SKE50122.

<5> KAR 22 1970-1 52-3 (H Gough) (OS Card Reference). SKE45264.

<6> KAR 35 1974 150 (P Couldrey) (OS Card Reference). SKE45310.

<7> Kent Underground Research Group, 2005, Caves and Tunnels in South East England - Part 17 (Unpublished document). SKE25124.

<8> English Heritage, List of Buildings of Special Architectural or Historic Interest (Map). SKE16160.