[1] The "sinews of" something was a classical metaphorical usage for the core or indispensable basis of something (LSJ s.v. neu=ron I.2: web address 1). For the specific notion of wealth or money as the 'sinews' of war or battle, see also mu 380 (citing Pindar); Plutarch, Agis and Cleomenes 48; Appian, Civil Wars 4.99, etc.
[2] George of Pisidia, Heraclias 1.163-4 Tartaglia; on Heraclius during his incursion into Persia, undeterred by the rich spoils the enemy had acquired in their earlier plunder of Roman territories; cf. Tartaglia (205, note 40). On Heraclius, see generally eta 465.