What’s the origin of the phrase ‘Tower of strength’?
This term derives from The Book of Common Prayer, 1549:
“O lorde… Bee vnto them a tower of strength.”
Shakespeare later used it in Richard III, 1594:
‘The king’s name is a tower of strength.”
Meaning
Someone who can be relied on to provide support and comfort.

This term derives from The Book of Common Prayer, 1549:
“O lorde… Bee vnto them a tower of strength.”
Shakespeare later used it in Richard III, 1594:
‘The king’s name is a tower of strength.”
Historical trend
Source: Google Books Ngrams (1820–2020).