“tenor of the emperor's writ”
'Tenor' here means the exact substance or purport of a document — the precise terms it contains, not merely its general drift. A 'writ' is a formal written command issued under authority; 'the emperor's writ' is the official written order from Augustus to the Senate. The First Senator is reading out its exact contents.
- TLN 2151historical topical
“Pannonians and Dalmatians, And that the legions now in Gallia”
Pannonia (roughly modern Hungary and Austria) and Dalmatia (the Adriatic coast of the Balkans) were volatile Roman frontier provinces. Under Augustus and his successors, they required heavy troop commitments — most dramatically the great Pannonian revolt of 6-9 AD, which Suetonius calls the most dangerous crisis since the Punic Wars. This explains why Rome must raise a supplementary levy of gentry: the regular legions are tied down elsewhere and cannot be pulled for a British expedition.
historical Ancient Britain and the Roman tribute “He creates Lucius preconsul”
A proconsul (spelled 'preconsul' in this text) was a Roman official appointed to govern a province or command an army with the full authority of a consul, the Republic's chief magistrate. By Augustus's time the emperor could 'create' — formally appoint — a proconsul to lead a specific military campaign. Caius Lucius, already commanding forces in Gaul, is here given supreme authority over the British war.
historical Ancient Britain and the Roman tribute“whereunto your levy Must be supplyant”
'Supplyant' is an unusual Shakespearean form meaning 'supplementary' or 'filling the deficit' — the new gentry levy must make up the number needed to bring the weakened Gallic legions up to strength for the British campaign. The word is not 'suppliant' (a petitioner) but a distinct formation from 'supply' meaning to reinforce or complete a deficient force.