Battle of Thermopylae 480bc - the Phocian Wall

The picture of the Phocian Wall so far is clear, it was a stone wall some 12 feet tall with a parapet wall along the top and a gateway on its landward end. But there is a serious problem as to its actual site. On the southern end the wall would have been built flush to the almost sheer mountainside, but at the northern end the sea gave a much less secure flank. The coast here was one of sandy beaches, and it is impossible to build a stone wall on a sand beach without it collapsing in the first storm to hit. Any attackers would simply need to wade into the sea to their waists and walk around the right flank of any wall built at the Middle Gate.

Clearly the Persians did not succeed in doing this, so the Phocian Wall cannot have just stopped at the edge of the beach. The easiest solution would have been to bend the wall back as it approached the sea. This would have meant that any troops seeking to outflank the wall by walking in the waves would have exposed their vulnerable, shieldless right side to the defenders. The wall need have been built back along the shore for only about 50 metres or so to be effective.

Alternatively, the builders of the wall may have relied upon temporary defences to render the surf impassible to hostile infantry. It would have been relatively easy to make wooden fencing, bristling with thorns. Weighted down with stones, these would have remained in position in the sea for some weeks before being washed away and were easily replaced when they did. Such a barrier would not have been impassable to determined men, but it would have been a slow job to cut it down with axes. The defenders would, of course, have used this delay to inflict casualties on the men seeking to cut a way through the fencing.

from THE BATTLE OF THERMOPYLAE by Rupert Matthews