Portus GPR & the Amphitheater

Portus GPR and the Amphitheater
Portus GPR and the Ampitheater

Portus 500 MHz GPR results showing various features in the area of the amphitheater and Imperial Palace

I have been recently churning out some text and figures for an up-and-coming publication of last year’s Laurence Seminar at Cambridge University on “Archaeological Survey and the City”. (There’s a link to my presentation on the ‘presentations’ page, if interested) The Portus gang gave a series of talks during the seminar on everything from the range of geophysical techniques used on site and within the surrounding region, to the 3D visualization that has played a large role in the on-going interpretation of the Roman port complex.

No real breaking news here, other than to have another excuse to post a recent figure I concocted for the publication which I thought was of note. The image is an interesting one (to some of us..) as it displays some of the GPR (500 MHz Sensors and Software) data from 2007 alongside the ongoing interpretation and excavation data from the 2006-2009 seasons. A great deal of the ground from this survey area was excavated in the last season, further shedding some light on the GPR data.


Interesting findings:

The large area to the West of Building 1 (part of a cistern complex) turned out to be a the floor (in the style of opus spicatum) of a room (whose function is still under debate) which connected the cisterns on either side of the trackway.

Bits of the walls of the so-called amphitheater were also revealed in the GPR data very early on, including what seemed to be 3 concentric walls under the modern trackway. It was confirmed through excavation in the 2009 season that the amphitheater indeed had a third (previously unknown) outer wall, connecting it to the adjoining room block.

The Claudian mole which runs along the northern edge of the excavation was also seen to continue underneath the modern trackway as noted in the large east-west, high amplitude feature.

Should be noted:

The modern trackway (containing a series of gravel deposits extending up to circa 1 meter below ground) which bisects the Imperial Palace at Portus resulted in (multiple) very high amplitude reflections throughout the slices in this area, making some interpretations of other anomalies somewhat tricky.

Some of the north-south and east-west walls in Area E (excavation area to the West of the track) did not show up so clearly in the GPR data. The traverses of this survey were conducted in an east-west direction, perpendicular to some of the walls in question. I’m convinced the issue lies with the survey line resolution (0.5m spacing with walls less than 0.5m wide) combined with the survey direction, probably leading to patchy results in this area.


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