The altar originally comes from the Cycladic Greek island of Delos in the Aegean. Delos grew rapidly in the mid-2nd-early 1st Century B.C. with its wealth based on commerce, being made a free port in 166 B.C. The island was also an important religious centre with its principal sanctuary of Apollo.
These altars were not only used as dedications in the sanctuaries of the gods, but also in private houses for domestic cults and for deceased family members. Cf. R. Ling, Classical Greece, Oxford, 1988, pp. 116-117 for a similar altar in situ on Delos in Serapeion C which was one of three sanctuaries established to Egyptian gods during the Hellenistic period. Also, L. Budde and R. Nichols, A Catalogue of the Greek and Roman Sculpture, The Fitzwilliam Museum, Cambridge, 1964, pp. 41-42, nos. 71-72, for two altars from Delos of a similar type.
A legacy of the Grand Tour, the fashion for using these altars as garden ornamentation in 18th and 19th century English stately homes was not uncommon. Five similar altars reside in the gardens of Wrest Park in Bedfordshire, reputedly bought by the Countess de Grey from Topham Beauclerk in 1817. Cf. D. Noy, 'From the central Aegean to rural England', Minerva, vol. 21, no. 3, May/June 2010.