Stones with a square cross-section bearing Roman numerals have been set in the ground in several places in Thompson's Park. They mark historic land boundaries and relate to the 1912 land transfer from Charles Thompson to the Cardiff City Council. Originally there were stones numbered from 1 to 17 and these can be seen on copies of Parks Department plans held in the Local Studies section of the Cardiff Central Library. There are plans dated 1911, 1912 and 1933. An (undated) document describes the locations of the stones and the boundaries of the land transferred to the Council in 1912 with respect to the adjoining properties. The 1912 plan is reproduced below and it shows that The Dell was excluded from the original gift. The 1933 plan relates to the transfer of ownership of The Dell in that year, and it shows some of the boundary stones in new positions - these are also shown on the plan below.
Ordnance Survey maps after 1940 included the positions of some of the stones, but without their numbers.
Unfortunately not all the stones appear to exist these days. Taking an anti-clockwise walk around the park from the northerly (Pencisely Road) entrance, stones 14, 13, 5, 6, 7, 8, 9, 10, 3, 2 are encountered in that order. In the vicinity 2 and 3 is an additional stone (possibly number 4) buried such that only its top face is visible. Stones 1, 4, 11, 12, 15, 16 and 17 are unaccounted for..
The photograph below shows Stone 8 in the foreground and in the distance is Stone 9. These are in the positions shown in blue on the above plan. The path on the easterly side of the park is seen winding its way up hill through The Dell, eventually reaching the north entrance.