Nobody knows what happened immediately after the Romans arrived in 43 AD, because no Roman fort has been discovered in this part of South East England. Time Team are on a mission to find the missing link. Local archaeologist Paul Wilkinson believes he has already found a military ditch, which would surround such a fort. It's a prime site, right next to Watling Street. However geophysics cannot find any evidence for a ditch. So begins one of their most frustrating digs, directed by Neil Holbrook. Phil enlists in the Ermine Street Guard for a day. They are joined by Roman expert Tony Wilmott and pottery specialist Malcolm Lyne.

• Tim Taylor

• Suzannah Lipscomb
• Tony Robinson
• Phil Harding