The porta praetoria, the porta decumana, the porta principalis sinistra and the porta principalis dextra.
At the Lunt, archaeological excavations have uncovered the porta principalis sinistra, or the eastern gateway. The porta praetoria was beyond the limit of the excavation site, underneath the pavement and road surface. The porta principalis dextra lies underneath the garden on the Carousel bungalow. The porta decumana has most likely been lost through erosion on the north slope down to the river.
The Royal Engineers reconstructed the Porta Principalis Sinistra (eastern gate) in September 1970. The design was based on examples from Trajan's Column in Rome and was consistent with the archaeological evidence for a double gate with no guard chambers.
The size of the six main postholes suggested that the gate would have been between 9.15m and 10.65m high.
Various factors which would have influenced the design were taken into account, including local weather conditions, the width of the roadways, the availability of timber and the status of the site.
The end result was a two storey, unroofed, double gate with planked doors. Ladders led from the fighting platform to observation platforms. These were enclosed by balustrades with cross bracing, a standard feature of Roman military architecture.
It was discovered from this experiment that it would take 10 men using a single pole with pulleys and guidelines to easily haul the individual sections into place. The gateway took three days to reconstruct.