Exactly when humans settled in Hatfield is still open to debate and discovery. Hatfield's earliest recorded mention in history is found in the Cotton manuscript, written on a Gospel belonging to the Diocese of Ely, and lists people who lived in the area. As Hatfield was only given to the then Abbotts of Ely (the Bishopric or the office of Bishop of Ely was created in 1108) around 970 it is likely that it was written between 970-1085 AD.
However, there is evidence that humans had lived in the area a lot longer – Middle Stone Age flints have been found. But who can say what else is still waiting to be uncovered.
Old maps show that there were swallow holes in the area for centuries but there doesn't appear to be any evidence as to exactly how long they have been there (with porous chalk one passage could collapse and another open at any time). However, if they existed at the time of early man they are very likely to have been a source of wonder.
An early human settling down for the night by a large lake which disappeared by morning is likely to have been harrowed by fear and wonder. Or may be just following a stream and finding it apparently disappears into the Earth could have aroused superstitious fears. So it is quite possible that swallow holes had a spiritual significance to early humans.
But the jury is still debating as to how early.