De Bello Gallico 3.12

3.12.1Erant eius modī ferē situs oppidōrum ut posita in extrēmīs lingulīs prōmunturiīsque neque pedibus aditum habērent, cum ex altō sē aestus incitāvisset, quod bis accidit semper hōrārum XII spatiō, neque nāvibus, quod rūrsus minuente aestū nāvēs in vadīs adflīctārentur.

The positions of the towns were generally such that, set on the ends of spits of land and headlands, they could not be reached on foot when the tide had rushed in from the open sea, which always happens twice in every twelve hours, nor by ships, because when the tide ebbed again the ships would be wrecked in the shallows.

Note. bis … hōrārum XII spatiō: the tide comes in twice every twelve hours (in fact about every twelve and a half).

3.12.2Ita utrāque rē oppidōrum oppugnātiō impediēbātur.

So the attack on the towns was hindered in both ways.

3.12.3Ac sī quandō magnitūdine operis forte superātī, extrūsō marī aggere ac mōlibus atque hīs oppidī moenibus adaequātīs, suīs fortūnīs dēspērāre coeperant, magnō numerō nāvium adpulsō, cuius reī summam facultātem habēbant, omnia sua dēportābant sēque in proxima oppida recipiēbant: ibi sē rūrsus īsdem oportūnitātibus locī dēfendēbant.

And if ever they were overcome by the size of our siege works, when the sea had been shut out by a mound and dams and these had been built up to the height of the town walls, and they began to despair of their fortunes, they would bring up a great number of ships, of which they had an abundant supply, carry off all their belongings and withdraw to the nearest towns: there they would defend themselves again with the same advantages of position.

Note. sī quandō: 'if ever'. The imperfects dēportābant, recipiēbant, dēfendēbant describe what used to happen.

3.12.5Haec eō facilius magnam partem aestātis faciēbant quod nostrae nāvēs tempestātibus dētinēbantur summaque erat vāstō atque apertō marī, magnīs aestibus, rārīs ac prope nūllīs portibus difficultās nāvigandī.

They did this all the more easily for a large part of the summer because our ships were held back by storms, and sailing was extremely difficult on a vast and open sea, with great tides and few, almost no, harbours.