That pottery can be dated, and so tell you the date of the city itself. By dating the pottery of all the settlements along the ancient lost branches of the Nile, that will tell you when each settlement was inhabited. And therefore, when that particular branch of the Nile was active.

Every kind of pottery or ceramic has a unique signature that dates it in time, the type of clay, the way it was made, the techniques of firing and glazing, can all be pinpointed to specific periods.

Nowadays it is possible to date within approximately thirty to fifty years accurately by ceramic alone.

So by combining his map of the ancient waterways with his knowledge of dating pottery, Bietak was able to pinpoint where and when the Nile flowed through the delta at each moment in history. What's more, the amounts of pottery along the old river beds would tell him where the biggest ancient settlements were.

Just as Montet would have predicted Bietak found that one of these branches of the Nile known as the Tanitic Branch ran directly past Tanis where Montet had found Piramesse. The problem came when Bietak dated the settlements along this branch.

Here is Tanis and this is the course of the Tanitic Branch of the Nile, with numerous sites along its banks, but no site of dates from the time of Ramesses the Second."

Which means this branch of the Nile didn't even exist at the time of Ramesses the Great.

"This eliminates the Tanitic Branch of being active in the time of Ramesses (the) Second, also it rules out that Tanis had been Piramesse"

What Bietak had discovered was extraordinary. There was no pottery at Tanis from the time of Ramesses the Great, all of it dates from at least 200 years after his death. This meant that despite all of Pierre Montet’s genuine finds, the great pharaoh couldn't possibly have built his capital city here. Tanis contained lots of ancient pottery and Montet assumed that like all the statues and obelisks at the site, it also came from the time of Ramesses the Second.