What he did not realise was that the treasure trove of more than 100 items – including gold and silver jewellery, ingots and a unique enamelled cross – was one of the most significant Viking hoards ever discovered in Scotland.
When the spot where Mr McLennan, 47, made his original find was fully explored, an archaeologist unearthed a silver cup containing more items wrapped in cloth.
The contents of the Carolingian cup, engraved with animals and one of only three known in Britain imported from the Holy Roman Empire of Charlemagne and his successors, are still to be X-rayed and their provenance revealed.
The discovery, the largest and most important Viking treasure found in Scotland since 1891, was made while Mr McLennan was exploring fields owned by the Church of Scotland in Dumfries with fellow detectorists the Rev David Bartholomew and the pastor of Elim Pentecostal Church, Mike Smith, both from Galloway.
Mr McLennan said he was rendered speechless at what he had unearthed two feet beneath the ground – well below the depth his machine should pick up a signal.
Among the items was the early Christian solid silver cross with enamelled decorations, thought to date from the ninth or tenth century.
Mr McLennan, who thinks the decorations could represent the four evangelists Matthew, Mark, Luke and John, said: “I believe they resemble the carvings you can see on the remnants of St Cuthbert’s coffin in Durham cathedral. For me, the cross opens up the possibility of an intriguing connection with Lindisfarne and Iona.”
Experts said while the hoard shares elements with other spectacular Viking age finds, this new hoard is of international interest because of its unique mixture of gold, silver, glass, enamel and textiles.
Church of Scotland trustees have reached an agreement with Mr McLennan for an equitable sharing of the reward when the hoard’s value is assessed.
Other items include a golden bird pin, silver stamp-decorated bracelets from Ireland and beads commonly found in Scandinavia.
Mr Bartholomew said: “It was tremendously exciting, especially when we noticed the silver cross lying face-downwards. It was poking out from under the pile of silver ingots and decorated arm-rings, with a finely wound silver chain still attached to it.”
Fiona Hyslop, the culture secretary, said: “It’s clear these artefacts are of great value in themselves, but their greatest value will be in what they can contribute to our understanding of life in early medieval Scotland, and what they tell us about the interaction between the different peoples in these islands at that time.”