The Archer Tower is a wall-defense building. Builds Lv1-50, each level requiring Keep 6 plus a matching Walls level for early tiers (Walls 2 at Lv2 through Walls 50 at Lv50); from Lv7 also the matching Keep level. No Unlock column, so no troop-tier/Blazon unlocks. Key milestone: Duty Officer at Lv11 -- the earliest duty-officer slot among these buildings (increases Archer Tower Attack, i.e. wall-defense damage; ideal Ban Chao, Themistocles, Maurice of Nassau). Costs: Lv1 900 food/900 lumber; Ore at Lv12; Lv25 ~9.8M/12M/13M/13M; Lv50 ~35B/44.2B/44.2B/45.7B. Power 15 (Lv1) to 70,000,000 (Lv50). Speed +0% to Lv17, +30% at Lv18 to +610% at Lv50. The Archer Camp requires matching Archer Tower levels for several upgrades (Lv27/30/32/35 and every level 36-50), so Archer Tower level is a prerequisite for high-level Archer Camp progression. For a bot: treat as a wall-defense asset; the cheap Lv11 duty-officer slot is an easy early buff, and keep it leveled to unblock Archer Camp upgrades.
Original research source: Evony Guide Wiki