Answer:
Soldiers must be wary of their enemies.
Step-by-step explanation:
In the excerpt, after Odysseus's men think they've won, they let the fugitives go in land. The fugitives then go get the Cicones' army. The army comes down to the beach and wipes out Odysseus's men. Since Odysseus's men underestimated the enemy, they are destroyed. Therefore, the best theme of this excerpt is that soldiers must be wary of their enemies. Even though the men do reap the benefits of their initial victory by gaining stores of wine and mutton, they do not leave the beach alive. The fugitives are not isolated because they have an entire army the run to for help. The only mention of horses is that the army can fight on horseback or on foot. This is not enough to develop a theme.