Crypto Infrastructure
Layer 2 doesn't replace the chain. It bundles the work above it.
When too many people transact at once, a blockchain gets congested and fees rise. An extra layer executes transactions above the main chain and reports them back bundled — cheaper and faster, and carrying assumptions of its own.
The problem
Six transactions. Send them the slow way first.
Every one of them wants a slot on the base layer. The trilemma lesson named layer-2 and rollups as the active work on exactly that squeeze — here is the mechanism.
Two layers, one set of transactions
BASE-LAYER SLOTS USED 0Six transactions are waiting. Press Send them one by one and watch the base layer fill up.
Illustrative model — six is a count chosen to make the mechanism visible. This lesson describes bundling, not throughput: no transaction rates and no fee amounts are claimed here.
Not every transaction has to run on the base layer individually. A Layer 2 executes many of them on an extra layer above the main chain and publishes them together — that is batching. Rollups take it one step further: many transactions are compressed into a single base-layer transaction, and the cost of that one entry is spread across everyone inside it. More transactions fit through, fees fall and applications respond faster — which is what makes areas full of small transactions, such as DeFi, gaming, digital collectibles and payments, practical day to day.
Both halves are true at once. A rollup inherits security from the layer beneath it: the bundled data travels back to Layer 1, and that return trip is what the bundle rests on. It is also a system of its own, with parts the base layer does not have — a sequencer that orders transactions, bridges in and out, upgrade keys. Cheaper and faster? Yes. Risk-free? No. Layer 2 moves the load off the base layer; it does not hand you scaling for free, and it does not repeal the trade-off the trilemma described.
The definition
Three things a Layer 2 actually is.
Tap each card for what sits behind it.
Hands on
Two rollup families, the same three questions.
Switch sides. Neither column is the winner — they differ in when correctness is established.
Optimistic rollups
ASSUMED CORRECTBoth families do the same job: execute above the main chain, bundle, post back to Layer 1. The split is about how correctness is established, not about whether the base layer is involved.
The bridge
Execute, bundle, post back — and what that trade costs.
Five steps, in order. The last one is the half that marketing tends to leave out.
This is the follow-through on the trilemma: scaling on top of the base layer rather than loosening it — the load is moved, not abolished. That leaves two threads open. A bridge connects separate networks; a Layer 2 scales one of them. The next lesson puts both together as cross-chain infrastructure.
Check yourself
Five questions.
Answers come straight from this lesson. Submitting completes it.