A419 Bridge
A419 Bridge.

This new crossing probably coincides with the ancient Cricklade crossing of Irmin Street.

1087:Calcutt (Colecot) in The Domesday Book
ODA of WINCHESTER (one of the Kings Thegns) holds CALCUTT of the king. — There are 5 hides. In the time of King Edward it paid geld for half a hide. There is land for 3 ploughs. Of this 4½ hides are in demesne. There is 1 villan and 4 bordars with 1 slave have 1 plough; and [there are] 60 acres of meadow. In Cricklade 3 burgesses pay 21d. It is worth £4.

1692: Baskerville, Harleian MS -

Criclad Bridge.
On Wiltshire side, begins hard by ye bridge houses, where is a foot bridge built of wood for people to go over in time of floods, which has 22 Passes for water between ye Postes.  The ye Casway on which horses travail in time of floods hath 9 passes for water.  But 2 passes are small and then you enter into Creeklad on this side 3 streams of water run through these passes viz: Those passes of the timber bridge, and those 9 passes of water in ye stone Casway. 
The biggest streame is called the River Rey.  Its top springs rise at Wroughton commonly called Roughton.  Thence it descends on ye west side of Swindon to Shaw, Redborne, and then to Cricklad.
  The 2d streame rises in Bradonfforest & thence descending by Purton, runs to Cricklade, or Crekelade.
  The 3d not fur or else a dead stream.  The Bridges and Casway to go into Glocester shire from Cricklade are 580 paces or yards long, to the farther side of ye bridge over that stream which comes from Cyrencester [the Churn].  The other stream runs by Ashton Canes comes in by Cricklad Town.  The 2d Bridges viz That Bridge over Ashton Canes stream, and that bridge over Tems or Cyrencester stream and ye casway between, have 12 arches for water to pass.  But ye Casway wch leads from Tems Bridge to Latton in Glocester shire (a  mile fro' Cricklad Town) has no Arches.

So make of that what you can.   Notice Baskerville is evidence for Seven Springs as the true source and not Thames Head. He calls the Cirencester Stream "Tems", and the other source "the Ashton Canes Stream".

View under A419 -

under A419
View from under A419 Bridge towards Cricklade.

The noisy A419 dual carriageway road has a large, wide concrete bridge.  Underneath it the river flows over a concrete bed. The bridge is new enough that the river has not yet silted up the width beneath it.
Water meadows with view of new housing in Cricklade to the South.

1683: Hannibal Baskervile -

At the head of this stream (Crickladd stream which meets the Tems at Crickladd) a gentleman of my name well skilled in the art of conveying water, Mr. Thomas Baskervile, who now lives with the Lord Ward at Dursley Castell in Staffordshier, Hee did propose to the Lord Chancellour Hide a feasibility of uniting ye Avon and Temes and so to make good a Navigation for Boates from Bristoll and Bathe  up the river till they got to Tems and then downstreame to Oxford and London.
This gentleman in [16]81 takeing my House in his way from London homeward, I fell into discourse with him concerning this thing.  Hee told mee there was a possibility of doing it;  and that if ever it were done there would bee such a stock of water in the Dikes that the River Tems should never want water, but bee supplyed from thence for navigation in the driest Summer.

1692: Going downstream Thomas Baskervile (Hannibal's son?):

So farwell Cricklad, come off yt ground,
We'el sail in Boats, towards London Town,
Ffor this now is, the highest station,
By famous Tems for Navigation,
But when th 'tis joyn'd with Bath Avon
Then row your wherrys farther on,
Ffor Baskervile, Matthews were Projectors
Who did conclude, sixty Thousand Pound,
Would thoroughly open, each river ground,
Ffor by power of lockes, Rains, & ffountains,
They'l make Boats to dance, upon ye mountains.
But further yet, to ease your minde
How these great works, were then design'd,
Here read their Book, there you will see,
'Twas possible, such things might be.

River Key, Left bank -

River Key
Fifty yards above the A419 bridge the River Key joins from the South.

Cricklade, Haslehurst, 1906
Cricklade, Haslehurst, 1906
© Oxfordshire County Council Photographic Archive; D230585a