The Monumental Brasses of St. Mary's
There were two monumental brasses that are documented as being found in the Church of St. Mary Belchamp Walter. These have sadly been removed and only the stone matrices (Incised Slabs) remain and are in poor condition.
The account of the brasses are taken from the Essex Society for Archaeology & History Transactions - Vol VIII Part 1, 1900.
First Matrix
The first brass is the matrix (the stone slab) that once had the brass of a man in armour and a priest in the Church of St. Mary's Belchamp Walter.
The text from the Essex Archaeological Society" - "Some Interesting Essex Brasses".

Text and plate from: Transactions of the Essex Archaeological Society
Vol III part 1 - 1900
Two Essex Incised Slabs.
By Miller Christy And E. Bertram Smith.
Second Matrix
The second incised slab is supposedly "exceedingly worn". Never-the-less it is now under the carpet in the central aisle of the Church.

The identities of those memorialised
While we will probably never know who these were, we do know that a descendant of Sir John Gernon was married to a son or grandson of Robert_Swynborne.
Joan Gernon was married of Sir John de Botetourt who ( or his grandson) are memorialised in the chantry chapel that was in the church.
The vicar (priest) in 1403 was John Crispe (according to Church records):
Church records: - the church guide
William Smythies recorded that John Crispe was the priest in 1403 and is most likely to have been the incumbent at the time of the installation of the tombs and brasses. If the two individuals were brothers the soldier was associated with Colne Priory.
Update: November 2024
When the tomb matrices were inspected by Martin Stuchfield the first matrix is definitly that of Sir Robert Swynbourne and his brother, the priest of the parish at the time John Crisp.
If this is the case the date of the Chantry Chapel would be dated to the middle to late 15th Century. This would be just later than the estimated dating of the Medieval Wall Paintings (being arond being 1440)
Sir Robert Swynbourne and Sir John de Botetourt, 2nd Lord, both fought in the Hundred Years War. Their armour is indicative of the period.
Other interesting brasses at Brightlingsea
Are also described in the ESAH article.
A third tomb in the aisle
A floor memorial to Anne Raymond with of John Eden, daughter of Oliver and Frances Raymond.
Anne was one of Oliver and Frances' Twenty One children she was first married to John Lawrence. She married John Eden at an unknown date, the date on the memorial is 16??.
Sir Robert Swynbourne in Lancastrian armour
Newcourt's Repertorium
Full Title:
Repertorium Ecclesiasticum Parochiale Londinense: Comprising all London and Middlesex,
with the parts of Hertfordshire and Buckinghamshire to the said diocese belonging
Richard Newcourt, (died 1679) was an English topographical draughtsman and cartographer. He reproduced effigies of the clergy that had been found memorialised in tombs and brasses. He is quoted by the EASH article about the incised slabs.
Richard Newcourt was a was a friend of Sir William Dugdale, and drew some views of religious houses, which were engraved for Dugdale's Monasticon Anglicanum.
INCISED SLAB AT MIDDLETON, ESSEX, TO SIRE JAMES SAMSON, RECTOR OF THE PARISH, WHO DIED IN 1349.