had built these two forts with which to protect the _chevaux de frise_.

"The battle of the Brandywine, as you may remember, was fought on the
11th of September, and, as I have said, the British pushed on to
Philadelphia and entered it in triumph on the 26th."

"Papa, what are _chevaux de frise_?" asked Grace.

"They are ranges of strong frames with iron-pointed wooden spikes," he
answered; then went on:

"In addition to these, the Americans had erected batteries on the
shores, among which was the strong redoubt called Fort Mercer, which,
and also Port Mifflin on the Mud Islands, I have already mentioned.
Besides all these, there were several floating batteries and armed
galleys stationed in the river.

"All this troubled the British general, because he foresaw that their
presence there would make it very difficult, if not impossible, to keep
his army supplied with provisions; also they would be in more danger
from the American forces if unsupported by their fleet.

"Earl Howe, as you will remember, was at this time in Chesapeake Bay
with a number of British vessels of war. As we have just been doing, he
sailed down the one bay and up into the other, but was prevented, by
these fortifications of the Americans, from continuing on up the
Delaware River to Philadelphia.

"Among his vessels was one called the _Roebuck_, commanded by a Captain
Hammond. That officer offered to take upon himself the task of opening a