I do not know this song's origin or time period. I do know that it's a traditional piece. I also do not know the setting in which it would be sung, but I suspect it's likely a drinking song. I could find no sign of it in my search of the internet. The chorus is reapeated at the end of every verse.
Come draw up the line, my people
The days of peace have passed
Put your gear in readiness
The host is closing fast
They think they can prevail
But they know not the strength they're fighting
Before we give our land up
We will perish to the last man
Hold them fast at the river
Guard the ford right well, my people
Here we draw the line, stand side by side
Turn back the tide
Our fathers won this land
From the elements and nature
Bent the banks and built the dike
To hold the floods of spring
We will not let their toil and blood
Be wasted by invasion
So stoke the bonfires, tramp your watch
And let them hear you sing

Now again the time has come
To gather at the ford
To see the glancing torchlight
Gleam on halberd, helm and sword
Fast and sharp, our foes will find
The temper of our mettle
They would plunder, let them come
To take their just rewards

Come draw up the line, my people
The days of peace have passed
Put your gear in readiness
the host is closing fast
They think they can prevail
But they know not the strength they're fighting
Before we give our land up
We will perish to the last man