The oldest Irish term for a set of weapons is gaisce, a compound of two separate words: ga “spear” and sciath “shield”. This reflects the fact that in Iron Age and Early Medieval Ireland a warrior’s basic military equipment consisted of a shield for defence and a spear for offence. Experienced fighters probably supplemented this duo with a second spear, for medium-range throwing or close-quarters combat, while some may have also carried items like small stabbing-knives, leather slings with pebble shots, or even wooden clubs. It has long been assumed that only the very wealthy made use of swords, initially very short thrust-and-cut weapons that were eventually displaced by lengthier swords under the influence of even longer Continental and then Scandinavian examples, a limitation which was thought to have lasted into the Middle Ages. However that presumption has latterly been called into question and it may be that swords were also available as secondary or tertiary weapons to even those of relatively modest means.
Throughout the first millennium CE, Irish shields were probably far smaller than most of their European counterparts. In fact they were probably closer in size to the later Medieval buckler, with a similar design and use. That is, a lightweight round deflector for use against violent thrusts or stabbings, held by the hand or forearm behind a round central boss or a slightly conical boss in later centuries, its size favouring speedy movement and agility in hand-to-hand combat. Modern depictions or reenactions of Irish fighters carrying large Continental- or Scandinavian-style round shields – or worse, so-called kite shields – are likely wrong. Especially when we know that late-arriving Viking communities around the Irish Sea partially adopted Ireland’s preferred outsize buckler-type at an early stage. That said, anomalous designs have been found in the early Irish archaeological record, medium-sized oblong shields similar to but not the same as some Roman types, challenging the convention that circular shields dominated the manufacturing process in the country from the Bronze Age to the Middle Ages (albeit with variations in materials, designs and sizes).
As a final note on Irish shields, while we can fairly deduce that they were of lightweight wood, we cannot specify with certainty what other materials were used in their construction. Small, centrally placed metal bosses were likely, initially round and later slightly conical under English influence. A riveted metal rim seems probable. But was some type of cattle hide or treated leather used as a covering over the wood? Early Irish literature seems to indicate so but this claim has been challenged by some modern scholars. And were the shields decorated, using ornamental studs or limewash, perhaps with animal patterns? The evidence is balanced both ways, depending on your interpretation of some textually difficult and usually late manuscripts.
Below are some interesting discussions of shields and the main variations we encounter in the historical and archaeological record from some of my favourite history-focused YouTube channels.