Experts from the University of Leicester discovered paving stones which they believe belong to the garden of Robert Herrick, where it is recorded there was a memorial to Richard III.
Work so far has involved the digging of two trenches at a Leicester city car park, and this week a third was excavated – thought to cover the site where the former king is believed to have been buried in 1485.
Working with members of the Richard III Society, archaeologists also said they had found the church of the Grey Friars.
Research at the site, which is owned by Leicester City Council, began on August 24, with archaeologists using ground-penetrating radar equipment to mark out the trenches.
Philippa Langley, of the Richard III Society, said: "This is an astonishing discovery and a huge step forward in the search for King Richard's grave."